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Posted By Topic: Separated supply motorhome

Rhino
Sep 11 2017 14:01

Isolated inverter (separated supply) to single socket (single load) inside connectable installation (motor home).
Coming directly from inverter just like fig 4.1 (B) asnzs 4509.1. note one indicates RCD for (B) by the position of the note however the drawing doesn’t suggest this.
Aszns 3001 2.2.7.5 suggests RCD on every circuit in connectable installation.
For this set up RCD or no RCD?

   

AlecK
Sep 11 2017 15:13

The set-up you describe is neither a connectable installation nor a standalone installation. So neither Standard covers it.

Being a separated supply, no RCD is necessary 9and if you fit one, you'll have trouble testing it.

RCDs are "additional protection" ; when the primary protection is by automatic disconnection of supply in the event of a fault.
With separated supply, you're not using automatic disconnection but one of the other permitted fault protection methods (see clause 1.5.5 of "3000"), and adding an RCD won't provide a significant improvement of safety. On the other hand, it won't do any harm - except maybe to your wallet.
   

Rhino
Oct 03 2017 12:13

If the cable for the power point was hard wired into the inverter I understand a double pole breaker would need to go in between the powerpoint and the inverter. What if the inverter was of the plug in type and one end of the cable is a male socket that plugs into the inverter and the other end of the cable/cord is hardwired to a powerpoint, (eg ext cord cut in half going directly to a fixed socket outlet) would you then also need to place a double pole breaker inbetween the power point and the inverter?
   

pluto
Oct 03 2017 13:58

Rhino Oct 03 2017 12:13

Your comment

If the cable for the power point was hard wired into the inverter I understand a double pole breaker would need to go in between the powerpoint and the inverter. What if the inverter was of the plug in type and one end of the cable is a male socket that plugs into the inverter and the other end of the cable/cord is hardwired to a powerpoint, (eg ext cord cut in half going directly to a fixed socket outlet) would you then also need to place a double pole breaker inbetween the power point and the inverter?

My comment

What useful purpose is the double pole circuit breaker going to provide? It would provide an isolator in the output of the inverter, but so would the removal of the plug from the inverter, but one could use a double pole switch instead for isolation purposes.

If you was thinking that it would provide a usful overcurrent protection for the inverter it would NOT do so, it would be too slow in operation if the double pole breaker was of the correct rating to remove the inverter loading in the case of an loading overload.

All good inverters will have their own electronic based overload protection which will be matched to the maximum output power or current and would operate in a very short space in time so as to prevent electronic compontent damage.

So in most cases the need for an external cicuit breaker is not required.

In some cheaper low specification inverters the output voltage collaspes and provides no output voltage nor output current.
   

Rhino
Oct 26 2017 20:06

A little bit confused - Two connectable installation (3001) topics regarding the same situation - independently wiring a PowerPoint to a “230V plug-in isolated type inverter” using an extension cord cut in half. Eg one end of the cord plugs into inverter and the other end hard wires into the socket outlet.

Topics in forum - 1. “RCD required on isolated inverter” and 2.“Separated supply motorhome” seem to come to different conclusions..

1. “A fixed socket outlet supplied from a plug would meet the definition of a connectable installation. Therefore it must be wired in accordance with "3001", including max demand limitation and RCD protection.

To avoid that sort of complication, just use an extension cord.”
2. The set-up you describe is neither a connectable installation nor a standalone installation. So neither Standard covers it.

Being a separated supply, no RCD is necessary 9and if you fit one, you'll have trouble testing it.

RCDs are "additional protection" ; when the primary protection is by automatic disconnection of supply in the event of a fault.
With separated supply, you're not using automatic disconnection but one of the other permitted fault protection methods (see clause 1.5.5 of "3000"), and adding an RCD won't provide a significant improvement of safety. On the other hand, it won't do any harm - except maybe to your wallet.

Just looking for clarification around this situation as I thought with an isolated supply (separated supply) the RCD would not be required?

A Similar situation to the above however now the inverter is independently supplying the entire motorhome. Fig 2.1 in 3001 shows an RCD required but notes that it will not be effective unless used with an earthed supply. Fig 2.1 also details a removable supply lead so I understand the RCD is there when the supply is changed to an earthed supply. However, what if the detachable supply lead is completed removed and now the motorhome is being supplied solely by the isolated inverter. EG the inverter output is to be hardwired from the inverter to the MSB to supply power points and lights etc, with no option to plug in to a service pillar/shore supply.

Would the MSB have “no MEN link and no RCD protection” OR would the MSB have “an MEN link and RCD protection”?

   

AlecK
Oct 27 2017 10:12

I think I mis-read your OP in this thread (focussing on "single load" rather than "single socket"). And I was not precise enough when i said 'not a standalone installation". Leading to an apparent conflict between answers.

The "rules" are written with two intentions
- to cover the "normal" range of configurations; and
- to prevent any unsafe abnormal configurations.
They don't always deal well with unusual set-ups; and sometimes they prohibit or require particular methods in the interests of "keeping things simple" instead of trying to cover every possible set-up and make particular rules to cover it.

An example is that while use of separate supply is a valid option for fault protection under "3000" 2.4.1 ; it isn't currently accepted under "3001" for (new)transportable structures - which are required [3.3.2] to have RCD protection for all final subcircuits.

So I'll try to cover the range of possibilities and how the "rules" apply. Hoping the dreaded "Forbidden" error doesn't strike. In each case, I'll assume the inverter is isolated output and everything is in a relocatable structure (eg caravan).

1 inverter socket > load (with or without ext cord).
Not a connectable installation. Not part of any installation. No PEW. Just fittings used as designed. No particular rules apply. Safe because separated supply; equivalent to same load supplied from mains via isolating tx. Adding RCD would not significantly increase safety (and couldn't be tested by normal methods).

2 inverter socket > i/2 ext cord > fixed socket outlet.
Socket being fixed is installation wiring, so is PEW. Capable of receiving external supply (plus other factors) so meets definition of connectable installation (in Act), and must comply as per ESR 60. As above, RCD doesn't add significantly to safety (when used on the inverter) - but is required as part of compliance.

3 inverter (socket or direct-connect) as alternative supply for mains-supplied connectable installation. Is part of connectable installation, must comply. Isolated output inverter is part of compliance, but NOT because we want a separated supply. Instead because we want to limit the options to something we can then modify to mimic normal (MEN-type) supply; so that everything works as if plugged into mains.

4 inverter socket used as source for connectable installation supply lead. Inverter is not part of CI, so - despite "3001" 2.4.1 - no "rules" on type. Because source is not part of the connectable installation, inverter / generator "requirements" in 2.4.1 and Figs 2.1 & 2.2 are guidance; not backed by any ESRs requirement. Note in Fig 2.1 is not quite correct; most RCDs will still detect & operate on current imbalances 30 mA or more. But on the isolated supply would require dual faults to create such - so doesn't meet fundamental requirement for fault protection by auto disconnection: to operate on occurrence of fault [3000" 1.5.5.2(a)]. And testing RCD difficult(pushbutton will work, but normal RCD tester won't). But safe because fault protection is by separated supply; and compliant because doesn't breach any ESR--backed Rule (including that subcircuits have RCD protection).

In practice no rules can effectively control source that's plugged into. Can only effectively control what is done by licenced electrical workers; ie fixed wiring.

5 inverter directly connected as sole supply to fixed wiring in relocatable structure.
- No capability for external supply, so not a CI, so 3001 does not apply.
- Not a property, so not an "installation" (as defined in Act), so "3000" need not apply.
- meets definition of "standalone power system ("note: "system", not "installation"); so IF wired to "3000" Part 2, must comply with "4509.1" [ESR 60] .

Assume choose to follow Part2 / 4509.

5a supply to single load. Can either have an earthed-neutral config (4.4.2) or a separated supply (4.4.3). Since inverter has isolated output, simplest is separated supply. No N-E connection; and no RCD required.

5b supply to single switchboard within relocatable structure. 4.5.3 requires an earth electrode (remember "4509" is aimed at static, not relocatable). So not possible to comply. So abandon following Part2, thus releasing from having to follow "4509". Adopt Part 1 solution. OR (because not an installation at all) design from fundamental principles, using what guidance you can get from Standards but not being required to comply with anything other than ESRs.

----------------

I won't go into what happens with non-isolated outputs, just too complicated.


   

pluto
Oct 27 2017 10:33

There is an important point that you are missing, and that needs to consider is the system of supply that is used in transportable structures (or connectable installations in NZ).
A connectable installation has to be able to be supplied by normal mains as would be provided in a caravan park, and, if required, an alternative supply such as generating set or inverter.
The overcurrent protection provided on the final sub circuit(s) in the connectable installation must be able to operate in an electrically safe manner irrespective of the supply source.
AS/NZS 3001 is drafted on the basis that additional earth leakage protection is to be provided in the connectable installation by the use of 30mA RCDs. RCDs as you should be aware require an earth referenced supply to operate correctly and to disconnect the supply when earth leakage conditions are present automatically.
The use of an isolating transformer is not considered due to weight and cost considerations for the full-time use to convert the system of supply in the connectable installation to be a separated 9orm isolated) system of supply. The use of an isolated inverter is not a preferred option as it is difficult and expensive to get inverter having a separated (isolated) supply with a true separated (isolated) supply between the DC input and AC output.
If the connection is a socket outlet, the earth leakage protection has been detailed by AS/NZS 3000 and AS/NZS 3001 as being provided by30 mA RCD protection.
If the load is permanently connected, the use of a separated (isolated) supply to protect an individual item may be possible as for a single item earth leakage protection it is easy to provide a satisfactory level of earth leakage protection by some supply systems. This approach is NOT practical for the whole connectable installation system of supply.
Normal mains supply (or MEN) supply provides an earth referenced supply. The need to provide a common overcurrent and earth leakage protection in a common protective device means that the alternative supply must also be arranged to provide an earth reference output.
If you carefully look at figs 3.1 and 3.2 of AS/NZS 3001, you will find that earth referenced supply is being provided. in the case of Fig 3.1 this is an isolated supply, but the earth reference is provided by the changeover switch when in the generator(or inverter) position only.

   

AlecK
Oct 27 2017 11:51

When it comes to supplying (for example) 2 KVA, an inverter is probably bigger, heavier and more expensive than compared to an isolating tx or genset. Which means inverter supplies are generally only suitable for supplying small loads like phone chargers, TVs, etc. Even small inverters doing SFA need either big batteries to feed them, or a near-constant charging source. If you want an inverter supply to do real work like kettle, toaster or microwave, a couple of PV panels are not going to keep up and you'll need a huge battery.

And if all you need is somewhere to re-charge your phone, easier to keep it separate from the 'connectable installation'. KISS.
   

Rhino
Oct 27 2017 18:11



The bus is going to have a 3000W inverter (isolated type) inside connected to a well sized $4000 battery bank with a battery monitoring system that will protect the battery’s and disconnect the DC loads (including the inverter) if the batteries are discharged below a set point -50% DOD. There are adequate solar panels on the roof to top the battery’s up all year round also as a backup and while driving the bus engine will allow the alternator to top the battery’s up.
The 3000W inverter is to supply a MSB in the bus which will supply final sub circuits such as PowerPoints and 850W element in HWC.

I think AlecKs comment below sums the situation up well thanks;

“5 inverter directly connected as sole supply to fixed wiring in relocatable structure.
- No capability for external supply, so not a CI, so 3001 does not apply.
- Not a property, so not an "installation" (as defined in Act), so "3000" need not apply.
- meets definition of "standalone power system ("note: "system", not "installation"); so IF wired to "3000" Part 2, must comply with "4509.1" [ESR 60] .

Assume choose to follow Part2 / 4509.

5a supply to single load. Can either have an earthed-neutral config (4.4.2) or a separated supply (4.4.3). Since inverter has isolated output, simplest is separated supply. No N-E connection; and no RCD required”

As I understand there are two options (correct me if im wrong)

Option 1; no MEN link in MSB, no RCDs, Double pole circuit breakers throughout MSB.

Option 2; MEN link in MSB, RCD protection for all circuits(RCBO as mains switch) single pole MCBs for subcircuits.

Note; earth bar is connected to chassis in both situations.

Which option would be technically safest and why? I think option 2 would be simplest.

   

DougP
Oct 27 2017 18:33

Apart from the electrical aspects Rhino, running a 850W water heater element off the battery (even a $4000 lithium I presume), isn't a good idea.

It will be drawing around 70+ amps off the battery for quite a long time. Which will be a lot more than the solar can replace. So the solar will need much more time (than the run time of the water heater) to replenish the capacity used.
   

pluto
Oct 27 2017 20:03

By ESR 2010 definition it is still a connectable installation so as/nzs 3001 applies and also WoEF will be required.

I would suggest that you double check the max solar output v's the maximum loading.

At a very rough check, I would think you will have a major short fall of generated energy on the likely loading.


   

Rhino
Nov 01 2017 22:53

The heating of the water is from gas mainly, however a water element is a back up and potentially going to be used as a dump load when excess power is produced as there is a good sized PV array. Not really practical/ necessary however customer is adamant for a back up and is well informed and aware of the systems limits.

Pluto comment:
In ECR 2010 it would be defined as a connectable installation.

My comment;
ESR 2010(7);"a connectable installation is one that is designed or intended for, or is capable of, connection to an external power supply"
This bus is none of the above it is not going to be connected to an external supply. Therefore i dont see it being defined as a connectable installation, However it sounds like it would come under 3001 anyhow being a "Transportable structure"(stand alone transportable structure)that isnt connectable.

   

pluto
Nov 02 2017 06:59

I you look at the definitions of an electrical installation in the Electricity Act 1992 you will find that your portable electrical installation is covered and hence a WoEF is a requirement.

from the Electtricity Act 1992
"electrical installation

(a) means all fittings

(i) that form part of a system for conveying electricity; and

(ii) that form part of such a system at any point from the point of supply to a consumer to any point from which electricity conveyed through that system may be consumed; and

(b) includes any fittings that are used, or designed or intended for use, by any person, in or in connection with the generation of electricity for that person's use and not for supply to any other person; but

(c) does not include any electrical appliance".
   

AlecK
Nov 02 2017 08:57

The bus is covered by ESRs, but is NOT an "electrical installation".
The words quoted by Pluto are an old , redundant definition. They are seriously out of date.

The current definition was introduced as part of the Electricity Industry Act in on 1 Nov 2010 - seven years ago. The reason for the change was to include off-grid set-ups as installations, which they weren't under the definition quoted by Pluto - because they don't have a "point of supply". Definition is now in two halves, one for installations that have a PoS and one for those without a POS

The bus wasn't an installation under the old definition, because it doesn't have a POS. It's not an installation under the new one either; because both halves of the definition relate to "a property"; and a vehicle or other transportable structure is not a property. Property is land.

The definition that matters here is different. "Connectable installation" is also defined in the Act. ESR 7 simply adds further detail as to the specific voltage level at or above which an item that matches the rest of the definition is a CI, and below which it is not. The definition and the voltage level in ESR7 need to be read together.
However Rhino is correct that because the key item for being a CI is being capable of external supply, a transportable structure that is not so capable cannot be a CI.

Important point: despite both terms using the word "installation"; a "connectable installation" is NOT a kind of "electrical installation". The best explanation I've come across was from Mr Morfee of Energy Safety; who has said that,"works" (electrical installations", "appliances", and "connectable installations" can all be considered as collections of "fittings" connected together.

So this standalone bus is not an 'electrical installation", and it's not a "connectable installation" either. Does not need to comply with "3001"; nor does it require a WoEF. In fact even actual CIs don't require a WoEF UNLESS they are about to be plugged into that external supply that they are capable of accepting.

But it is a "standalone power system" as defined in AS/NZS 4509. That term isn't defined in either the Act or the ESRs, so under ESR 4(2) the definition in the Standard applies. And ESR 60 (2) says that IF it is wired to comply with Part 2 of "3000", then it must comply with "4509.1" as well.

All of which means there's SFA that this bus "must" comply with, other than ESRs. But there's plenty of guidance ; in "3000", "3001", & especially "4509.1". Similarly it doesn't have to run at "standard low voltage" - but would be mad not to.


   

AlecK
Nov 02 2017 10:05

confession time: I've just said this bus will be a "standalone power system"; and in my first reply is aid it wasn't a "standalone installation". Note the different wording, my first response used an incorrect / unofficial term, and using that term led me to make an error based on the word "installation". Lesson: ALWAYS check.

So, assuming 4509 is to be followed, which bits, and what do they say about the question of separated supply vs RCD? Basically "4509" is aimed at buildings on a piece of ground, so this bus is actually out of its "scope". Accordingly the Standard calls for earth electrodes; which isn't practicable for a bus. The only bit that doesn't is the one Rhino already found:
4.4 STAND-ALONE POWER SYSTEMS DIRECTLY FEEDING A SINGLE A.C. LOAD. 4.4.3 allows use of separated supply - but since the bus won't have a single a.c. load this isn't much help.

Why not use separated supply for multiple loads? Because the more loads, the greater the chance of having two separate earth faults resulting in hazardous voltage between two bits of equipment.

All the rest of "4509" requires an earth electrode; because the writers just didn't cover what we might call a "transportable standalone power system"

So since this set-up falls into a gap that isn't covered by any Standard, what's the best option? I think it would be Rhino's option 2: feed the (isolated) output of the source(es) into a switchboard that has a N-E link, and fit RCD protection. This would be identical to a connectable installation operating on "alternative" supply; so can be shown to be electrically safe.

Ideally separate RCBO for each subcircuit; and if cost leads to using a single RCD , then 2-pole protection for each subciruit would offer ability to isolate any faults that cause "nuisance" tripping of the RCD. Would certainly recommend that for a boat, from bitter experience; but for a bus perhaps not.







   

Rhino
Nov 07 2017 00:02

Thanks aleck that cleared a lot up ;

So your comment
think it would be Rhino's option 2: feed the (isolated) output of the source(es) into a switchboard that has a N-E link, and fit RCD protection.

Would the above scenario require an independent inspection? As far as I understand ELV pv array =no inspection, stand alone mains is excempt from mains work = no inspection , because I would be doing main earth conductor from MSb to chassis would this mean that I need to get the work inspected ? Also if it was to become a connectable installation would it need an inspection or would that be done during the CIs ewof under 3001?
   

AlecK
Nov 07 2017 08:25

Nothing in your plan is high risk PEW, so no inspection required. The chassis connection is not a "main earthing conductor", there are no "mains" or "main earthing system", and ES say that ELV PV arrays are not PEW.
Basically what you'll end up with is a standard dual-supply motorhome, minus the external supply inlet and changeover device.
   

pluto
Nov 07 2017 10:34

A dual supply motorhome is a connectable installation and WoEF is required.

Just as I said so some days age!
   

AlecK
Nov 07 2017 16:49

Once the "shorepower" supply is removed it's no longer either.