OT: 2-pole Circuit Breaker in Single Phase Supply

kamenges · Jan 30, 2019

Originally posted by tragically1969[\b]:

...in the UK the Neutral conductor doesn't change colour through a Fuse or MCB

Very good. As it happens, this machine is destined for the UK so this is very relevant. Thanks.

Originally posted by JesperMP:

As long as we are talking about a control voltage inside a control cabinet, then the neutral is not interrupted by the circuit breaker for the live phase.

Click to expand...

Is this a requirement or is it more common practice, because:

Originally posted by JesperMP:

If there is a single phase supply going out of the control cabinet (very rare nowadays), then both phase and neutral are interrupted by the circuit breaker.

Click to expand...

I actually have this situation. I have a main enclosure receiving the plant 3-phase supply. I also have a remote enclosure (approx 2 meters from the main enclosure) with devices that require a 230V single phase supply.

So I have both cases: 230V single phase inside the main enclosure and 230V single phase leaving the enclosure. Since I need to use double pole breakers on the conductors leaving the enclosure I would like to use them on the single phase supplies inside the enclosure as well as long as I am not violating any standards.

Keith

LadderLogic · Jan 31, 2019

We do break the neutral of the incoming 3ph + N service by means of a 4-pole disconnect switch - considering the neutral is different from the PE in than the neutral may be grounded (and in most cases it is), while PE is grounded always.

However, when inside of the cabinet, the neutral is never broken; three-pole breakers are used for three-phase loads and single-pole for single phase (hot+neutral) ones. A special case are GFCI breakers our customers require for service outlets - those always break the neutral so the load side wires are both black.

One problem we encounter in the US when building machines for Europe - it is hard to find a wire manufacturer who produces the required light blue (turquoise) insulation distinct from darker blue required for the 24VDC circuits.

tragically1969 · Jan 31, 2019

LadderLogic said:
We do break the neutral of the incoming 3ph + N service by means of a 4-pole disconnect switch - considering the neutral is different from the PE in than the neutral may be grounded (and in most cases it is), while PE is grounded always.

However, when inside of the cabinet, the neutral is never broken; three-pole breakers are used for three-phase loads and single-pole for single phase (hot+neutral) ones. A special case are GFCI breakers our customers require for service outlets - those always break the neutral so the load side wires are both black.

One problem we encounter in the US when building machines for Europe - it is hard to find a wire manufacturer who produces the required light blue (turquoise) insulation distinct from darker blue required for the 24VDC circuits.

The blue is nowhere near turquoise, its just blue, i don't know if they publish a RAL or specific blue for it, example here:

https://p3connectors.com/2018/04/30/electrical-wiring-colours-standards/

kamenges · Jan 31, 2019

Originally posted by LadderLoigic:

One problem we encounter in the US when building machines for Europe - it is hard to find a wire manufacturer who produces the required light blue (turquoise) insulation distinct from darker blue required for the 24VDC circuits.

While I agree that "European neutral" blue is not turquoise, LadderLogic is correct about blues in the US. There used to be a distinction between various shades of blue. Back in the day (25 years ago) you could actually get three distinct shades that would allow for 24VDC (dark blue), the European neutral color (blue) and IS circuit blue (light blue). It is now getting harder and harder to get anything other than "blue" in whatever shade that takes on. My guess is that is is easier to get a "European neutral" blue in Europe since it is a definite use color. In the US it really isn't.

Originally posted by LadderLogic:

...considering the neutral is different from the PE in than the neutral may be grounded (and in most cases it is), while PE is grounded always.

And this gets into the whole color thing again. In EN60204-1 it appears that the conductor defined as the neutral conductor will always be blue regardless of whether that conductor is actually grounded or not, which follows what the guys in Europe have been saying. This is different than in the US, where white is reserved for GROUNDED neutral conductors.

Thanks for all the info, guys. I think this gets me where I need to go with respect to breakers, neutrals and conductor colors.

Keith

kamenges · Jan 31, 2019

Originally posted by LadderLogic:

A special case are GFCI breakers our customers require for service outlets - those always break the neutral so the load side wires are both black.

I just read this more carefully. Is this for a customer in the US or in one of the EU member states? This would seem to make sense in the US but not so much in he EU.

Keith

lfe · Jan 31, 2019

The neutral should always be connected to the ground in the transformer of the company or that of the electric supplier.

In the same way that all electrical supplies must be referenced to ground and never floating and that applies not only for three-phase and single-phase but also for the internal supply of the cabinets, for example at 120 VAC or 24DC.

kamenges · Jan 31, 2019

While I agree with this from a design perspective, it doesn't seem like EN60204-1 makes this a requirement. Based on that standard a floating neutral system seems to be perfectly acceptable as long as it is correctly identified. Unless, of course, I am reading things incorrectly.

Keith

lfe · Jan 31, 2019

Now I am no longer involved in electrical schemes, nor now I have access to the regulations and I do not remember if that was explained in EN60204-1 or in another one.
But years ago I had to pass several regulatory compliance controls for CE marking and this aspect of not to have floating supplies was mandatory.

It also involves a risk since the floating can, due to electrostatic or electromagnetic inductions, take voltages referenced to ground of thousands volts.

Typical case that for example a communication module or an analogue module is burned without a clear reason. Probably somewhere in the communication cable or the sensor cable or on the electronic board there was a spark to the housing.

LadderLogic · Feb 2, 2019

kamenges said:
I just read this more carefully. Is this for a customer in the US or in one of the EU member states? This would seem to make sense in the US but not so much in he EU.

This is a European plant and this requirement was explicitly listed in the design specification. Until this, we were never asked to do such a thing by any other customer whether in the US or in Mexico or in China.

nehpets · Feb 2, 2019

Just a little point of fact, in the 18th edition ieee regs there is no distinction between live and neutral conductors, they are both considered to be 'live' conductors and any double pole switching needs to be done with a 'linked' Circuit breaker, to achieve isolation. I don't have the regs book with me at the moment so I can't quote the regs number.

Steve

lfe · Feb 2, 2019

The general switch of the machine have to completely isolate the equipment, except the grounding, from the electrical network and therefore it have to cut also the neutral at the same time as the phase(s).

And emphasize that the first rule to comply when selling/installing a machine in the EU is the Machinery Directive 2006/42/EC , which goes further than just the rules on electrical installations.

OT: 2-pole Circuit Breaker in Single Phase Supply

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