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125a 3phase


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Regarding neutral currents on three phase systems, these can exceed the phase current in some circumstances, but are unlikely to exceed the capacity of the neutral conductor in most cases.

Consider the following example.


A 100 amp 3 phase supply, fully loaded with dimmers feeding incandescent lamps.

With all dimmers fully on, each phase will be fully loaded to 100 amps, and the neutral current will be very small due to the balanced load. There will be some neutral current since a fully on dimmer does SLIGHTLY distort the waveform.


Now turn down all the dimmers such that the lamps are much dimmer, this will reduce the phase current to about 50 amps per phase.

Under such conditions the neutral current can be as much as twice the phase current, but note that this is twice the reduced phase current of 50 amps, i.e. a neutral current of 100 amps. It wont be twice the full neutral current.


The American NEC does indeed require oversized neutrals, but some regard this as over cautious.

The NEC is far more conservative than UK regs. As an example, #14 wire which is similar to 2.5mm is limited to 15 amps in the USA, here we can use it at 25 amps, more in some circumstances.

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Consider scenario 3:

Phase 1 fully loaded with full on dimmers - contributes 100A to neutral.

Phase 2 loaded with 30% dimmers (around 50% current depending on dimmer law), the phase distortion will likely mean that this does not cancel against the neutral current from phase 1 but will add to it.

Phase 3 30A of cheap switch mode LED kit with little power factor correction.


We rapidly have a neutral current that could easily be 150 amps in the worst case scenario.

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Yep, plenty if ways to blow out a neutral, especially once discharge ballasts (or switch mode supplies) of the cheap and nasty sort come into play (And even some big names that should know better are guilty on occasion).


A big moving light rig can have scary amounts of triplen, and negative phase sequence currents flowing.


Consider also that most smaller venues will have rather more rig then they have power for it, and that pushing things a little is not exactly uncommon and does tend to leave most of the dimmers in use part open, and neutral overload is not exactly uncommon.


Last install I was involved with, we did in fact double up the neutral lines to the racks.


Regards, Dan.

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  • 1 year later...

I think the OP's talking about Snaplock connectors?


Pretty rare in my experience.. Can't I've seen any outside of modular dim/hot rack systems such as the ones below.






No reason not to use them on temporary systems, just might struggle to find anyone else who stocks them, should you ever need more.


Snap-lock are available in the UK although they are a horrible connector.

Not sure I can tell you where to get them as that may be misconstrued as advertising.


As for the Ceeform 125 Amps, I agree that if you are running that sort of power constantly you should be looking at Power-lock/Power-safe connections.


I would never recommend Cam-lock I'm afraid.

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