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Posted By Topic: Plasma cutter

Jun 04 2017 10:09

BOC Plasma cutter with Imax 27.4 Ieff 15.

Supplied with 15A plug. To be used in a school workshop.

I've read all the welder threads. Concluding that although Ieff isn't nonsense it's not recognised in our bible. Therefore a 32A outlet is the go.

Looking at the flex lead it appears to be 2.5mm. I'd have to upgrade this to be comfortable.

This isn't an exercise in money saving. As its a school there is a lot of H&S at stake.

How do I answer the question as to why BOC sell it as a 15A plugged appliance?


Jun 04 2017 10:19

Yes, and if your not happy with their reply, make a complaint with energy safety

Jun 04 2017 10:42

Surely it should be BOCC answering that question, rather than you.
Though I doubt they'll give the true answer, which is (probably) that they neither know nor care.

Jun 04 2017 18:08

If you ask BOC for an answer be prepared to have a shower to remove the excrement that will be deposited upon your person.
They will question your qualifications to even ask a question like that, and then they will attempt to blind you with science. But in reality they will not answer you.

A complaint to ESS may also result in some nameless person assigning some validity to I eff despite the requirement that the supply lead and firings be rated for I max.


Jun 04 2017 22:29

Donny, here's the answer I got from ESS a couple of months back.

(begin quote)
This type of appliance falls under AS 60974.1 and AS 60974.6 for arc welding machines. The rating of this type of machine takes into account the duty cycle of the appliance and the maximum effective supply current I 1eff which is calculated by the formulas below. Also I 1max would be considerably higher but only momentary. In most cases a 15A AS/NZS3112 is adequate and compliant with the standards for arc welding machines.

The standard must be marked on the rating plate to be able to apply that standard. If it is, I 1eff must not exceed the rating of the AS/NZS3112 supply plug or it would be deemed unsafe.

If no standard is marked and the rating is higher than the plug, ESR23 would apply and you would be right to deem it unsafe.

Testing to AS/NZS 3760 with the above rating information in mind would be sufficient for you to carry out an appliance test in confidence.

Depending on the age of the unit you may be able to request a Supplier Declaration of Conformity from the supplier that would list the standards it was originally tested to.
(end quote)

Jun 05 2017 12:09

I noted this in the manual of a boc welder the other day, page 28 of the manual linked below. The 15a plug is for demonstration only.

If you upgrade the flex, plug etc check the main switch, many of the Chinese ones only have a 10a rated rocker switch on them.

I can see the thought behind the thermal aspects of the ratings but would like to see proof from a manufacture before considering it an option. Not customers hate 15a plugs logic.

Jun 05 2017 13:33

"If no standard is marked and the rating is higher than the plug, ESR23 would apply and you would be right to deem it unsafe"

Obviously that particular jobsworth isn't actually worth his job.
ESR 23 applies regardless of any Standard; and the item is therefore electrically unsafe.

Jun 05 2017 16:42

Thanks all. The units is a brand new BOC Plasma40. It's tech manual says 27.4A, the operator manual says 18.8A - but also says plug it into a 15A socket.

I can only assume that the ESS conversations are not legally binding and therefore are worthless.

I will see if there is an option for a different unit - perhaps a 3 phase appliance. It's not exactly something often shifted around.


Jun 05 2017 20:13

Donny, the plasma cutter I was following up on was also new and had similar numbers. I advised the distributor, brought it to the attention of ESS and refused to tag it. Nothing more I could do.

Anecdotally, I heard that the owner is now running it from a 10A GPO on a homemade adapter. Apparently he doesn't use it at full power either. Yeah right!

Jun 06 2017 11:47

This farce illustrates quite nicely what is wrong with the New Zealand way of doing electrical regulations. There are multiple sets of rules in different places, with a hierarchy of righteousness.

Whatever one thinks of American electrical practice, they have the sense to have all the rules in one book, the National Electrical Code.

So in the USA, this lark about welders being too big for the plug wouldn't be a debate involving standards that no electrician has ever seen; Every electrician would answer that "yeah, there's a section about welders in the NEC". Article 630, for the curious.

(Of course, it's not actually a "national" code, as it is different state by state, but in any one state there is one book with that state's rules. No argument.)


Jun 06 2017 14:03

Nothing unclear about it in NZ rules.
The Act is primary law.
ESRs are secondary law.
ESRs call up Standards & ECPs as means of compliance.
In a few cases, the means of compliance is mandatory (making those ones effectively another layer of law), but mostly not.

For appliances (eg this plasma cutter), they must be electrically safe when sold / supplied or offered for sale / supply [ESR 80}. There are a number of methods available for getting to "deemed electrically safe.
While electrically safe" & electrically unsafe are not opposites, they are mutually exclusive; so anything that's electrically unsafe cannot be deemed to be electrically safe and therefore is NOT permitted to be sold / supplied or even offered.

ESR 23 lists a number of features that take an item directly to "electrically unsafe"; and this item fits squarely in one of them [item 1(g)]. No ifs or buts or maybes; it's unsafe.

There's no need to consult any other documents. Just a need for those in positions of authority to understand and correctly apply the rules; instead of spreading confusion.

So while there may be examples that demonstrate the alleged superiority of the "American way"; this isn't one of them.

Jun 07 2017 09:52

There are (IMO) ifs and buts for welding machines. The maximum current figure for the machine is not necessarily the 'rating' of the machine. This is a similar concept to the way a motor has a rating, but this is not the maximum current the motor can (or may) draw in normal service, it's how much it can tolerate used continuously. With motors this is referred to as utilisation factor, having a similar meaning to duty cycle when referring to a welder.

As far as I can gather the 60974 standard sets out quite specific installation methods with regards to circuit protection and other tests to ensure the unit does not exceed the duty rating, i.e. it needs to not operate for normal use, but operate if used at 100% duty (if not rated for it) for any period of time.

At that point you have to wonder if a plug-in installation would be suitable, as moving the unit to another plug with different protection settings would undo all the hard work in making the unit safe.

Jun 07 2017 18:21

The bad news for the ESS interpretation is that you can only use the referenced standard if there is no marked rating on the equipment.
Quite clearly this plasma cutter has a rating plate with detailed information on it.
The fact that the suppliers are being encouraged to ignore it by the people who are supposed to be enforcing the laws is concerning.

The analogy of an electric motor is rubbish and shows how low the level of supposed competence has become among some areas of the trade. Full load current is full load current and is the maximum that the motor can safely operate at. If it is more than 10 amps then a 10 amp plug is not electrically safe.

There are countless small compressors out there in the marketplace with a rating plate that clearly says 13 amps but they have a 10 amp plug. The excuse is " it's hard to sell them with a 15 amp plug".

Jun 08 2017 13:19

Hmm, so if it didn't have a plate, you can use 60974, and use a plug rated for the I_effective (that's what that standard says), and this would be 'electrically safe', and also comply with best practice as specified in most of the developed world.

But with the addition of a plate, with a maximum, and an effective rating, suddenly using the same plug would transform the machine into an electrical hazard of some sort. I'm having a few competence related doubts myself here. Especially as the word 'maximum' doesn't feature in ESR 23(g).

The maximum rating given is to allow the installer to select protective equipment that will correctly protect at the maximum current. For a motor, they don't go that route, but typically the contactor is rated AC-3, which is a shorthand way for the installer to know it will break the maximum current for an induction motor (roughly 600% rated). What the installer does not do is install wiring and connectors for the motor maximum current, i.e. they don't install a 6kW plugpoint for a 1kW motor. Because it doesn't (shouldn't) draw 6kW continuously.


Jun 08 2017 15:29

"The maximum rating given is to allow the installer to select protective equipment that will correctly protect at the maximum current."

That sort of thinking is fine for a permanently connected item of equipment.

But it is not OK for plug-and-play equipment.
The only protection in place for a socket outlet is fault protection, overcurrent protection of the cable supplying it, plus (maybe) an RCD. Nothing that can protect the equipment plugged in.
Which is why ESR 23(1)(g) exists; to keep plug-in safe. That equipment may or may not have internal protection systems, eg to shut it down if it internally overheats. But not all such gear has internal protection, and the user won't know (nor understand). So the ESR has to assume worst case.

Jun 09 2017 09:41

It doesn't say that, and it also does not, and logically can not, protect against all eventualities of that nature.

To labour the point, and to return yet again to the motor analogy, a 10 amp (rated) motor on a plug can easily be run at substantially higher currents. This is, of course, a misuse. The machine manufacturer is not liable for misuse, and nor is the installer of the plug point, or the person who tagged the appliance. There also is not a requirement to install to protect against any such misuse.

In exactly the same way, using a welding machine substantially above its rated duty cycle is both easily possible, and again, a misuse. In exactly the same way as for the motor, damage to the machine, and the installation, may result.

For the welder, it's easier to predict the maximum possible current drawn even through misuse, it's there on the plate. For a motor, you'd pretty much have to guess. Hence my assertion that the clause means what it says. Rated current is that specified by the manufacturer which the appliance can draw continuously, not the maximum the machine could draw for short periods, or (and) if misused.

While it is commendable to try to go the extra yard with safety, in this case I don't believe it's a requirement. In fact I would think that installing a higher rated plug, which then has higher rated circuit protection, will ultimately result in the welder or motor in a molten blob on the floor due to any hypothetical misuse. It may be preferable to install the correct rated outlet/plug with only a single outlet per protective device, rated within an amp or two of the outlet.


Jun 09 2017 11:10

The problem is a 10A breaker on the outlet would not allow the intended use of many “10A” devices. They are relying on the fact that the wiring is likely protected to a higher limit and give the outlet a hiding in the process.
From my Chinese mig, supplied with a molded 10A inlet I read on the ratings
180A output @ 21VDC - which is 3.8KW output. Let’s leave out reactive power, for simplicity here, it will actually make the situation even worse as it adds to the I2R losses.
Assuming .8 efficiency 4.7KW of real input power is needed. It claims to be able to do this for 4min on, 6min off. 20A is going to cause four times the heating of 10A.
If reliance on safe appliances (correct inlet connector for rating) was not used we’d need to put a breaker on each outlet to ensure that it was protected in the case of overloading by rogue appliances.


Jun 09 2017 11:16

The actual wording is "rating specified on the appliance"; so if only one ratintg is given (as with most motors) there can be no confusion. For a dual-voltage motor, with two ratings according to voltage, again no confusion which to apply.
So we're arguing (discussing) which "rating" if there is more than one but neither is obviously the "right" one.
You say I eff; most other say I max.

There is no definition of either "rating" or"rated current" in either Act or ESRs; so i.a.w. ESR 4(3), we need to look at IEC60050.
Specifically (Schedule 2) IEC 60050-826 Ed 2.
However while it's directly cited in ESRs, it doesn't seem to be available via EWRB "free" access. So while I believe you're wrong, I Can't prove it.

To follow your motor analogy, the usual rating given is FLC.
The equivalent for a welder is not Ieff, it's Imax - the full load current under normal conditions, but not allowing for fault conditions which could result in higher current.

Your arguments about duty cycle are valid for permanently wired equipment; where protection can be applied externally to ensure that if the duty cycle is exceeded, control devices will switch the motor off.

The same does not apply to plug-in equipment. Some welders have built-in protection, just as some motors have built-in thermal protection. For such cases it may be valid to use I eff or I cont. But in the absence of such protection, it can't be valid to use these, and the equivalent of FLC must be used - in welder terms; I max.

Note that there is one exception to this plug-rating rule, and that's for ranges. CLEaRLY THE WRITERs WERE aWaRE OF THE FacT tHat some equipment is capable of drawing more than the rating of the plug; and made specific allowance for one particular instance of this. They made NO such allowance for any other type of equipment - NO mention of welders, or compressors, or plasma cutters, or anything else than a free-standing range - and then ONLY if it complies with the applicable Standard.

We have to consider the entire ESR, not just one particular paragraph; and when interpreting the ESR as a whole the fact that these other types of equipment don't get any dispensation must be regarded as significant.

Accordingly I don't believe using I eff, or any other "rating" than max that can be drawn under normal operation (disregarding duty cycle)is either appropriate or compliant for plug-in equipment.

Welders are DMRAs, so an SDOC is required; and the "welder" standard has to be complied with. But a plasma cutter is not a welder (as defined; so we get no help from a welder Standard WRT a plasma cutter.


Jun 10 2017 07:16

IEC 60050:442 (Electrical Accessories) defines current rating as follows:

"the current assigned by the manufacturer for a specified operating condition"

Where you say the equivalent of I_max (welder) is I_rated (motor), I disagree. I_rated for a motor is the current it can take continuously without overheated or sustaining other damage, in other words the manufacturers designed usage. For a welder, I_max is the current it can sustain temporarily, if such current is subject to a duty cycle designated by the manufacturer. The I_eff is the current setting that the welder could sustain continuously without likewise overheating or sustaining other damage.

@gregwires - I think your welder has not got the correct plug. Does it show a rating I_eff on the plate or in the documentation?

The method for calculating I_eff is:

(((I_weld^2) * duty cycle) + ((I_rest^2) *(1-duty cycle)))^0.5

Using 22.4A for the welding current (assuming ~10% voltage drop) and 0.5A for the idle current, this works out around 14.15A, in which case a larger plug is definitely required.

Jun 10 2017 08:12

Tspoon a motor drawing 10A under normal conditions is required to have automatic overload protection by section 4.13. This requirement is not met if the motor overload protection is simply asking the operator to adhere to a duty cycle.

So applying Ieff only works to protect the circuit automatically if the welder has internal overload protection that includes enforcing the duty cycle. I suggest that welders intended for home use are unlikely to have that protection.

Jun 10 2017 09:24

While true, many motors (plugin style, for home use) also do not incorporate any cutout. In this case, the same as for plugin welders, the basic common sense, and ability to follow instructions, of the user is effectively the line of defense against mishap and gross overload of wiring and outlets. I'm not saying that's a great idea, but it is what it is.
We don't put plugs onto motor appliances that are larger than the appliance rating in the expectation that the appliance will be misused, even though it may well be. This is the general principle that I believe is extended to welders, when I try to interpret that particular reg. That this interpretation is in line with the IEC method gives a measure of support to that line of thinking.

Jun 10 2017 20:25

It seems like we have to go back to basics again.
The protection installed in the switchboard is to protect the fixed wiring. And at a pinch maybe a fixed wired item on a dedicated circuit.

The only protection for a plug in device is a correctly sized plug and lead rated for the load.
So up to 10 amps for a 10 amp plug and so on for each larger size of plug.

If someone overloads a 10 amp rated motor and the protection required by 4.13.2 or the standard that the device is manufactured under does not work then that is a fault, and should be repaired.

If the rating plate has current ratings on it you must use the highest one to select the appropriate plug.
ESR 23 does not care about duty cycle.

I have seen enough melted plugs because of decisions made by people who thought that they new better.
Home handymen and tradesmen in NZ are notorious for overworking their equipment and fitting a smaller plug for convenience generally leads to a melted plug and socket.

Debate about the correctness of ESR 23 is irrelevant and opinions from ESS are simply not worth anything unless posted on their web site at a minimum. A notice in the gazette would be better as you could then cite it as a justification.

Feel free to lobby the people that write the rules if you want a change in the rules. But it won't happen through this forum.

And finally you can't use IEC60974 for a plasma cutter because it is not a welder. So once again the ESS solution is not available because there is no cited standard for plasma cutters in AS/NZS3000:2007.


Jun 11 2017 08:36

A plasma cutter is covered by 60974. From 60974-1 section 1.1 (Scope)

"This part of IEC 60974 specifies safety and performance requirements of welding power sources and plasma cutting systems."

It goes on to say: "This part of IEC 60974 (i.e. part 1) is not applicable to welding power sources for manual metal arc welding with limited duty operation which are designed mainly for use by laymen."

60974-6 applies to "power sources with a thermal cut-out device for manual metal arc welding with limited duty. These welding sources are mainly used by laymen."

60974-6 goes on to say it does not apply to sources incorporating frequency conversion.

So for our purposes, 60974-1 covers all welding equipment and plasma cutters, with the exception of non frequency converting arc welders designed (in the main) for home use.

Both standards specify the same method of determining the sizing of the supply coupler, and I_1Eff is the rating given.

There is also, if going this route, a requirement for the outlet to not be rated at less than the protection, and the protection size should be specified by the manufacturer. Obviously, if using I_1eff as your rating, the machine should also clearly conform to the correct section of 60974, most likely by a declaration on the plate or in the documentation.

Also, on the propensity for New Zealand tradesmen and members of the public for stupidity when using equipment, electrical or otherwise, I fully agree. It happens. Misuse is beyond the ability of an ESR to effectively prevent. Over-rating circuits and couplers won't prevent it, especially if over rated circuits are supplied by subsequently higher rated protection. Instead of smoking appliances there'll be bubbling molten appliances.


Jun 11 2017 12:29

@tspoon thanks. That's great info for those of usc who don't have access to the standards.

The requirement if going this route that the outlet is not to be rated less than the protection is interesting. Kind of hints at a dedicated welder socket outlet.

Jun 11 2017 12:40

In @gregwires example, if the 15A plug was on a 15A MCB then the duty cycle is under the time-current curve but not by much. Nuisance tripping would be likely in extended use.

Jun 11 2017 14:28

No worries, I learned a fair bit digging around in the standards in the process. For future reference, if anyone needs to find definitions from IEC 60050, it is one of the few in which the content is available online, here:


Jun 11 2017 15:44

Appreciate all the input.

I think a point to note here is it is a school environment. So 'abuse' of equipment is somewhat of a given.
Also a salient point is that workshop power-board is ancient and the protection is HRC cartridges.

Ieff (15A) is on the nameplate. If 60974 indeed covers plasma cutters then perhaps my best course of action is a new dedicated socket and RCBO.


Jun 11 2017 20:58

The whole problem with this argument is that the plasma cutter has a rating plate, therefore reference to the standard is not required or relevant. The plug must be rated for the maximum current that the rating plate has on it.

ESR 23 has several requirements for safety and the argument that the internal parts of the welder or plasma cutter might be rated less than Imax makes the appliance electrically unsafe at ESR 23(b) so no need to even for a plug to it.

Jun 12 2017 07:55

This argument hinges upon the correct definition for ‘the rating specified on the appliance’, as to whether I_max or I_1eff is the ‘rated current’. Neither the act or the regs provide a definition for ‘rating’, and users are directed to IEC 60050 for any required definitions.
From IEC 60050-151-16-08: rated value: value of a quantity used for specification purposes, established for a specified set of operating conditions of a component, device, equipment, or system
and IEC 60050-151-16-01:
operating condition: characteristic which may affect performance of a component, device or equipment. Note – Examples of operating conditions are ambient conditions, characteristics of the power supply, duty cycle or duty type.
From this we can see that I_1eff can correctly be considered to be ‘the rating specified on the appliance’, and plug rating can be sized accordingly, with or without a plate.
ESR 23(f) also applies: ‘the appliance is a single-phase integral plug device (other than an appliance intended for permanent connection to an installation) that has a plug that does not comply with whichever official standard listed in Schedule 4 applies to the device; or’
This means that the applicable official standard is the arbiter, in terms of single phase plugs, for any device which has a standard as mentioned.

Jun 12 2017 08:06

Take a look at C2.5.2.2 (AS/NZS3000) for maximum demand

100% of rated primary current.

It's pretty clear to me, look at the nameplate, assume worst case and put a plug on rated at that or better. It's not hard or difficult, it's common sense.


Jun 12 2017 09:17

Completely agree that the correct interpretation hinges on definition of "rating" (the word used in ESR 2323(1)(g). It doesn't help that it just says "rating" and not "rated current"; which opens up the possibility that it's the voltage rating that matters. I don't believe that for a moment, but the interpetation is available from the words used (a problem that is likely to emerge when you let lawyers write rules about technical matt4ers). So far all appear to agree that we're talking about current rating of one sort or another.

Also agree that ESR 4(3)directs us to IEC 60050. But not to part 151 as used by "tspoon"; the Part cited in Schedule 2 is part 826 "Installations". Which means we can't automatically take the definitions from another Part as "the" correct definitions, even though they may be relevant to at least some degree.
I'll accept the definition of "retd current" for now,; which means there could be several "rated currents" for different operating conditions. So the next question is "which operating condition applies?".

Applying the letter of the ESR, and assuming the men "rated current" and not some other rating (IP rating?); IF the tally plate has 2 (or more) current ratings then either can be used. But which one "should" be used? The IEC definitions don't help with this.

Rather we're inside the heads of the writers of the ESRs, and I believe the only clues they've given us lead only to the conclusion that the highest rating stated is the one we "should" apply. I accept that "tspoon's" interpretation is available, but I believe strongly it's the wrong interpretation; unsupported by any evidence within the ESRs. Whereas the fact that the only exception is an electric range (an item equally subject to duty cycle" and to diversity) points to Imax as the intent. Given that it's my ticket on the line, I'll continue to apply Imax; and advise other accordingly.

Don't agree that ESR 23 (1)(f) is at all relevant, because I've never seen a welder that was an "integral plug device" (see definition).

Jun 12 2017 10:04

The trail possibly gets a bit murky in C2, but the definitions supplied in C2.5.2.1 can help a little.

The value stated in C2.5.2.2 is 'rated primary current', which is defined in C2.5.2.1 (a), and (paraphrasing) is the marked rated input current for the machine.

However they also include a definition (b) for 'Actual Primary Current': The current drawn from the supply circuit during each welding operation at the particular heat tap and control setting used.

This suggests they are different things, and 'Actual Primary Current' appears to be the closest match to I_max, and is does not appear to be what is asked for, which is the 'rated' primary current. As no definition is given for the 'rated input current' from the definition in C2.5.2.1(a), in 3000, Act, or Regs, this sort of puts us back where we started.

Complicating the matter for a plasma cutter example, is that there are two sections, arc welder and resistance welders, but which does a plasma cutter fit under? My opinion (opinion only) leans towards the Resistance Welding section, as they provide a method to determine loadings for machines which incorporate a duty cycle, using the defined 'Actual Welding Current', or I_max.

Possibly ultimately you could use either section, as the duty cycle multipliers in C2.5.2.3(a)(ii) are those derived using the I-1eff formula posted earlier.

Jun 12 2017 10:43

Resistance welders is stuff such as "spot" welders, where there is actual contact between electrodes and materials being welded.
Plasma cutters use arc, similar to arc welding.
But App C simply isn't relevant, as Maximum demand is not the point. Max demand is about selecting a conductor to carry the expected current - which we then protect against any current higher than the conductor's CCC.

Ie you can use duty cycle to establish expected load on the circuit, and use a smaller cable - but then must protect the cable at no higher than CCC.

And - -despite ESR 4(3) - you can't use App C's definitions, which were aimed at this separate function of establishing max demand, as basis for interpreting ESRs. For the definitions in App C to have a wider application, they would have to be in Section 1.4; whereas they are clearly tagged "for the purposes of Paragraph C2.5.2", ie they ONLY apply to that (max demand estimation for welders)and not to anything else. There's also the Note; that the max demand calc using those definitions is intended to prevent overheating of subcircuit conductors, and doesn't ensure meeting volt drop calculations.

The intent of the writers of ESR 23 is what we're trying to establish; and App C can't help us with that any more than 60050 does. The primary intent can only have been to protect plugs (and sockets) from sustained overloading. The method is by requiring plugs to be of suitable rating. The question is whether duty cycle / diversity can be used for establishing this. Clearly it is specifically OK to do this for a range, because an Exception has been made. The logical inference from this single Exception is that it isn't OK for anything else.

Jun 12 2017 11:15

AlecK my 12/06/2017 10:04 comment was not in regards to plug sizing, more as an answer to gregmcc's comment regarding circuit sizing, a related issue. To be clear, I only used those definitions within the scope of C2.5, as they clearly state, to provide some clarity with regard to maximum demand and circuit sizing.

Jun 12 2017 11:34

Seems neither side can convince the other, so we'll probably have to agree to disagree - pending an amendment to clarify ES's intent.
Bottom line; we won't be held to account on this unless something goes badly wrong, in which case some judge will impose their interpretation.

Not the only area of ESRs where there's doubt, and several interpretations by ES don't appear to be supported by the words in the relevant ESR. So while we have to follow the letter of the law (as best we can); it's by no means certain that the letter of the law is actually consistent with the intent. For some issues, ES staff don't even seem to all have the same idea of what the intent is; with different staff giving different interpretations at different times.


Jun 12 2017 11:40

With regard to the exception made for the range, it seems from ESR 23, that the exception for a range only applies to 23(f), and only to ranges conforming to an applicable standard (4 listed), and therefore the requirements for 23(g) still apply to ranges. Would that be the correct interpretation? If it is, then a logical inference cannot be made on that basis. Unfortunately leaving us no closer to the intent of the Reg.

It is true that IEC 60050:826 has no definition for ratings of any sort, with the exception of 'designed rating' which is nowhere mentioned in ESR 23. Therefore you are correct in stating that we don't have a definitive answer, and are likely unable to find one. Your position of using I_max as the rating is correct from the viewppoint of 'you can't go wrong'. My stated position of 'You may not have to' also has merit for the reasons I've described, but ultimately we don't know the intent of the writers of the Reg.
The practice of rating welding machines based on duty cycle and maximum load is an established engineering practice, as evidenced by the contents of IEC 60974 and ASNZS 3000 section C2, but how that translates from large industrial production line machines to single phase domestic duty welder installation is certainly debateable.
Which ever path installers take, perhaps the only takeaway from this thread may be to rate protection at less than I_max and greater than I_1eff for dedicated circuits for machines with a duty cycle.

Jun 12 2017 12:10

From information provided by ES at time of introduction (1 Feb 2014), it's clear that the Exception in ESR 23(4) was supposed to refer to (g) instead of (f)... and after all whoever heard of a freestanding electric range" that was also a "integral plug device"?

Of course that sort of error doesn't help. Mr Morfee has been known to suggest we should stop picking fault with ESRs, and get on & find ways of making them work instead. But that won't help us avoid penalties for breaching the letter of the law. What little case law there is seems to take a very pedantic approach.

Jun 23 2017 12:00

I have advised against the use of the plasma cutter and that I'm unwilling to install a socket for it. Citing ESR23.

Although the IEC standard "may" allow this I'm not convinced the internal switches for the device will be rated at 30A. Nor that a 15A plug was designed to take pulsed 180% overloads continuously.

And most of all because its school kids holding the appliance.

Thanks again for all the civil, informative and healthy discussion.