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Posted By Topic: 6115 changeable from single to 3 phase

Nov 04 2019 09:33

We have a 32amp 3 phase N+E mobile dental clinic, no equipment in the mobile is 3 phhase, it is all single phase equipment and only on 3 phase for load sharing.

There are some remote schools that do not have 3 phase. So we want to run the mobile on single phase.

To make things easier I'll refer to the 3phase N+E as just 3 phase... but I mean 3P N+E

The mobile is fitted with a 3phase chassis PLUG in the side service locker, and it has a 25m 3 phase lead.

When on a single phase site the idea is to use a lead with a single phase plug (that connects to the school)and on the other end a 3 phase socket that connects to the mobile inlet.

L1 from the plug is joined to L1-L2-L3 in the socket.

Protection for the single phase cable will be provided by an IP56 single phase 32amp MCB (or RCBO) that is mounted next to the school outlet, so the most that can be drawn by the mobile on the single phase is 32amp.

Appreciate any feedback.

Nov 04 2019 09:38

Hopefully a picture of the type of 3 phase N+E chassis plug mounted inside the service locker of the mobile dental clinic is attached.

Nov 04 2019 09:43

the proposed configuration will be non-compliant and unsafe.

If you parallel the 3 phases so all are on one phase, the current in the N will be too high.

Whereas when the load is spread across three phases, the phase angle of the currents balances out so that the N current cannot exceed the current in the highest-loaded phase, and is generally much less.

Nov 04 2019 09:47

I understand that but if the outlet is protected by a 32amp MCB, then the neutral current is limited to 32amp.

I'd assume that even on 3 phase, if there were no current in L1 and L2, and 32amp on L3, then there is no phase cancellations, so the neutral is rated accordingly ?

Nov 04 2019 10:09

On a 3-phase supply, yes the n-currents balance out to at least some degree,. Worst case being onbe fully-loaded phase, and no load on the other two, so that current in N will be same as the loaded phase.

But with all legs being suplied by same phase, there's NO balancing, and the current in n will be the sum of the three phase currents.

Probably not all fully loaded, so let's assume that there's say 20 A on each leg. 3 x 20 = 60, so the N current will be 60 A, via a conductor & fittings rated at only 32 A. And the only overcurrent protection you have will NOT be sensing the N current; so after a while there will be a fire.

Either the Health department needs to arrange for the smaller, single-phase clinic to be rostered to this site, or the site has to be upgraded to cater for the larger 3-phase clinic.


Nov 04 2019 10:18

I think you are missing one important point.

At the school outlet, right next to the single phase outlet, RIGHT NEXT TO IT (I'm not shouting, just emphasising) is a single phase 32amp MCB.

The max current in the single phase is 32amp, you can't take more than 32amp because right next to the school outlet is a 32amp MCB that solely protects the 32amp single phase outlet.

Therefore the max current in the neutral is 32amp.

Nov 04 2019 11:23

yes, I accept that the mcb will limit the available current for whatever is plugged into that particular socket.
And that therefore the fact that under this config they won't be able to use all their loads at once becomes a management rather than a safety issue.

However from a compliance perspective there's nothing to prevent this adaptor from being used elsewhere, on a source that doesn't have such close overcurrent protection. Remember that this socket will / should have been installed to comply with NZS 6115; which like "3001" requires individual overcurrent protection for each socket rated no higher than the socket. Those requirements don't apply universally.
So - despite the fact that IF used ONLY with that particular socket, there's no problem of overloading the N - the adaptor is deemed to be electrically unsafe; in similar way to any adaptor that allows for more load to be used than the rating of the fittings that make it up. And therefore making it is not allowed. Nor is using it.

Nov 04 2019 11:36

Why not put a current limiting MCB in an appropriate enclosure in the adapter lead similar to what is done for caravans fed from domestic socket.

Alternatively why not put a matching 3 phase socket on the fixed installation with the phases linked and with the current limiting MCB adjacent. Would need to be labeled for any one trying to use for a 3 phase machine.

Nov 04 2019 11:57

“ Under this config they won't be able to use all their loads at once becomes a management rather than a safety issue..”

We have many months of data-logging the shows overloading is not an issue, just because they are 3 phase 32amp does not mean they use it all, our logging indicates peak currents of 35amps and that’s with the 2KW (10amp) HWC cylinder on, so we are going to load shed the HWC and anticipate peak loads of 25amps, and the peak loads are during compressor start up etc

On paper you can predict worse case higher loads but that is not what our logging is showing actually happens in the clinics.

I agree about the adaptor being able to be used elsewhere, the adaptor will be marked only to be used on outlets with appropriate end-of-line protection with supporting training and documentation.

Nov 04 2019 12:03

“ Why not put a current limiting MCB in an appropriate enclosure in the adapter lead similar to what is done for caravans fed from domestic socket.”
We thought about this but having a single phase breaker in an IP56 enclosure hanging off a lead that is plugged into a school outlet is untidy and possibly prone to be knocked and played with.
However we are contemplating fitting a 32amp MCB in line with the single phase lead at the socket end (the end that plugs into the chassis plug inside the service locker on the mobile) So the single phase will go via 32amp breaker inside the service locker, then into the 32amp 3 phase socket, that plugs into the 3 phase chassis mounted plug.

This seems like the most sensible thing to do as it will mean we don’t have to upgrade any of the school outlets with 32amp MCB’s


Nov 04 2019 12:50

The definitive decision is to fit a 32amp MCB on the single phase lead that goes to the mobile. The MCB will be at the socket end where it plugs into the 3 phase plug inside the services locker, so it will be secure inside a locker and weather proof.

This way we don't have to do any work at the existing single phase outlets at a dozen or so remote schools.
Cybre high 5 Frostybird... Cheers

Nov 04 2019 16:27

Thought of the current-limiter while out & about (doing a WoEF on a camper that has a 10A adaptor)- but frosttybird has beaten me to it.

Something else to be aware of WRT 3 phase supplies for mobile medical; some of the units that were supplied by third party for installation at schools were wired non-compliant;. Basically saved a couple of metres of conduit wire by taking only one neutral up shared between the 3-phase and single-phase circuits (so obviously not these schools) but didn't provide linked switching / protection.
Loss of N leads to losing the 0 V reference for all the single-phase equipment supplied from the 3-phase outlet - with expensive results.


Nov 04 2019 17:23

The best and only solution likely to comply is the use of a SECOND supply lead purposely made to connect a 32 amp single phase IEC 60309-2 plug, followed by an inline 32 A 30 ma Type A RCBO.

The 2 pole RCBO is needed to be within 600 mmm of the 32 A single phase plug.

At the dental clinic end a IEC 60309-2 3 phase +N+S cord connector.

One European RCD manufacturer markets in NZ a minimum rated IP 44 enclosure suitable for the RCBO to located for in-line use.

The supply lead could be 32 A 3 core or a 5 32 A core cable, the number of cores will dedicate were the phase cores are commoned together, at ther RCBO or the cord connector. .

This recommendation follows a new generation of adapter leads for connectable installations currently under development, and requires that the supply lead be in "one piece"hence that is why a SECOND supply lead is required and can be customized to suit the site conditions and the connectable installation connection arrangements.

While it is undesirable to use work arounds in some remote areas there will be no 3 phase supply and a work around is neceesary in this case.

Nov 04 2019 17:44

There's no current requirement for the supply lead to be in one piece though right?

We can't be responsible for making decisions now, where requirements _might_ change with some future edition.

Nov 04 2019 21:18

DougP Nov 04 2019 17:44
Your comment 1

There's no current requirement for the supply lead to be in one piece though right?

My comment 1
NZS 6115:2006 +A1+A2 clause 2.11 (a) "Of sufficent lenght to supply the connectable installation without the use of extension cords."

Your comment 2
We can't be responsible for making decisions now, where requirements _might_ change with some future edition.

My comment 2
It has always veen a requirement from the original issue of NZS 6115 in 2006, so it NOT something that is new..

Nov 04 2019 22:54

DouP may have been thinking that you were saying the lead had to be 'one-piece' i.e permanently wired at the mobile end, not disconnectable at the mobile end........

Nov 04 2019 22:56

Does IEC 60309-2 include the PDL 56 series ?

Nov 04 2019 22:58

" followed by an inline 32 A 30 ma Type A RCBO.

The 2 pole RCBO is needed to be within 600 mmm of the 32 A single phase plug. ..."

Why an RCBO ?, the outlet is already protected 600mm away by it's own NSZ6115 30mA RCD/RCBO. ?
Why not just a MCB ?

Nov 05 2019 09:03

Pluto's preferred solution is not the "only" compliant solution. It certainly is not required now.

Two issues; so first the "in one piece" requirement. Doug is correct that we do NOT have to take any notice of what may be coming in future rules. What we have to do is comply with the current rules.

ESR 60 requires compliance with Part 2 of "3000" and "6115; and in turn "6115" requires compliance with "3001".
"3001" clause 5.1.1 requires supply leads to "be in one length"; and "6115" does not vary this.

However this requirement does not - in fact cannot - prohibit the use of an adaptor, or an extender. The legal requirement is applies to the CI itself, but cannot control how the CI is used. Pluto's suggested 2nd lead assumes that either the lead is detachable from the CI, else there may be multiple leads with a selector switch providing isolation between them. Each of those leads is 'in one piece" (else it isn't a complete lead!). So each is compliant.
But there is NO rule that prohibits use of extenders or adaptors. The "in one piece" rule has existed from long ago (was in 1976 Regs), and was originally intended to avoid having joins in leads made with (then) non-IP-rated plugs & connectors. But it has always been an unenforceable crock; and these days serves no useful purpose.

True "6115" requires the lead to be long enough to use without extension cord; but - like 3001 - it can only control how the unit is built and not how it is used.

Consequently the adaptors that have been widely available for plugging into a 10 A "3112" socket are perfectly OK, as long as they include current limitation to 10 A max. They are electrically safe. They are "in one piece". And while they do not comply as a "supply lead" under Section 5 of "3001", they can be used because there's no requirement for a CI to only ever be plugged directly into a fixed socket outlet. Never was. And not likely to be. So plugging into another lead, or an adaptor, is NOT illegal in any way.
And if done with due care - like having adaptors checked along with the WoEF check, and keeping a non-IP rated adaptor indoors - perfectly safe.

Which brings us to the 2nd issue; the idea that an RCBO is needed in the 2nd lead. That's NOT the case. Overcurrent limitation is required if any of the plug and / or flex has a lesser current rating than the connector. RCD is NOT required.

The config recommended by Pluto has been suggested for next edition of "3001" - but has not been endorsed by the Committee. Even if it does become a requirement, that will be some way off; not before the expected update of citations in ESRs due late this year. The draft is expected to come out for Public Comment soon, hopefully before mid-December but possibly not until Jan. When it does, you'll all have the chance to have your say on this issue - and others.

Actually there's a 3rd issue in Pluto's posts, though not directly relevant to YeahNah's problem. Pluto says the connector of the (detachable) lead must be a "60309-2" type. Balderdash. "3001" allows for three types of connector (obviously must match the inlet type), and "6115" does not vary this.

Lastly: "does IEC 60309-2 include the PDL 56 series"
Answer: some few items in that series comply with IEC 60309-2; eg the caravan outlet. also there's a 110 V outlet. But most of the 56 series complies with AS/NZS 3123 ; ie the normal type of industrial plugs, sockets 7 connectors in NZ & Oz. The "60309-2" items are identified in the catalogue (from memory an asterisk leading to a note).


Nov 11 2019 14:37

Thanks everyone....
One of the remote schools has 2 phase available and if possible we'd like to scope using both phases for load sharing.

Is there any problem with fitting a 3 phase N+E wall outlet, but with just 2 live phases.

Can we have a 3 phase plug lead with a 3 phase socket with L2 in the socket looped to L3

Alternatively can we loop L2 to L3 on the back of the 3 phase wall outlet, so long as the outlet is marked appropriately, if we can then we can use the same 3 phase lead as we would use for a 3 phase site. ?

My guess is if we do this we'll need a 32amp MCB in each phase wire of the lead.

I won't be a game changer if we can't but given the 250+kms to these sites we want to mitigate as much as we can.

Nov 11 2019 21:28

I know it's not what you asked originally but have you thought about having a 3phase inlet and a 1phase inlet and a changeover switch?