Another genset question

John- · Mar 21, 2021

Hi.

excuse my ignorance. I have seen this before. Why is the phase in this picture taken through two of the poles in this manner?

the isolator is wired in exactly the same way with the phase going through line contact out the top and back through another pole.

what am i missing please?

thanks

john

James · Mar 21, 2021

John- said:
Hi.

excuse my ignorance. I have seen this before. Why is the phase in this picture taken through two of the poles in this manner?

the isolator is wired in exactly the same way with the phase going through line contact out the top and back through another pole.

what am i missing please?

thanks

john

You might have forgotten to add the picture.

Darkwood · Mar 21, 2021

Without the pic' as expressed it might be difficult to respond although if we are talking about a 3 pole contactor with overload then it may be the overload monitors 3 poles and has balance and/or loss protection so in the case of single phase you have line and neutral and an empty pole, looping the line gives an output on each pole for the overload to recognise...... if it's not this then need that pic.

John- · Mar 21, 2021

darkwood said:
Without the pic' as expressed it might be difficult to respond although if we are talking about a 3 pole contactor with overload then it may be the overload monitors 3 poles and has balance and/or loss protection so in the case of single phase you have line and neutral and an empty pole, looping the line gives an output on each pole for the overload to recognise...... if it's not this then need that pic.

Ohhhh bugggah. Sorry. Attached now

John- · Mar 21, 2021

John- said:
Ohhhh bugggah. Sorry. Attached now

Darkwood · Mar 21, 2021

Without details of the actual breaker we cannot be sure but most 3ph mcb's do not give balance monitoring so this is purely for redundancy, they could have easily just fitted a 2 pole option here, however if the breaker has phase loss monitoring then that is why, the schematic symbol used in each pole does not suggest that is the case so I think it is just convenient redundancy or the designer doesn't fully understand the functional concept of a MCB.

Rockingit · Mar 21, 2021

darkwood said:
Without details of the actual breaker we cannot be sure but most 3ph mcb's do not give balance monitoring so this is purely for redundancy, they could have easily just fitted a 2 pole option here, however if the breaker has phase loss monitoring then that is why, the schematic symbol used in each pole does not suggest that is the case so I think it is just convenient redundancy or the designer doesn't fully understand the functional concept of a MCB.

Agreed - strikes me that it's not an MCB but just an isolator, though why you'd spec a 3p when a standard 2p would do it beats me.

John- · Mar 21, 2021

darkwood said:
Without details of the actual breaker we cannot be sure but most 3ph mcb's do not give balance monitoring so this is purely for redundancy, they could have easily just fitted a 2 pole option here, however if the breaker has phase loss monitoring then that is why, the schematic symbol used in each pole does not suggest that is the case so I think it is just convenient redundancy or the designer doesn't fully understand the functional concept of a MCB.

Thanks for the comment. It is single phase. And why did the installer fo the sane in the 3 pole isolatet located a few feet away?

[ElectriciansForums.net] Another genset question

Rockingit · Mar 21, 2021

That's a new one on me! Totally pointless.

Darkwood · Mar 21, 2021

Our replies would be better if the schematic reflected the actual install, that is not a circuit breaker as denoted on the schematic, that is an isolator, having said that if the cover is yellow it will denote it is for emergency isolation, in said cases where possible it is good practice to utilise spare poles for redundancy in these circumstances but it shows poor initial design if deliberately done in design, many of these isolators are off the shelf and they tend to stock 3 or 4 pole so purchase convenience is often the reason we have spare poles.
Without seeing the whole schematic or down stream devices I cannot comment on whether the isolator should actually be a circuit breaker in this case.

Rockingit · Mar 21, 2021

darkwood said:
Our replies would be better if the schematic reflected the actual install, that is not a circuit breaker as denoted on the schematic, that is an isolator, having said that if the cover is yellow it will denote it is for emergency isolation, in said cases where possible it is good practice to utilise spare poles for redundancy in these circumstances but it shows poor initial design if deliberately done in design, many of these isolators are off the shelf and they tend to stock 3 or 4 pole so purchase convenience is often the reason we have spare poles.
Without seeing the whole schematic or down stream devices I cannot comment on whether the isolator should actually be a circuit breaker in this case.

I think there’s so many variations on symbols for switches/isolators it’s hard to make that distinction?

pc1966 · Mar 21, 2021

It is often easier to get SP or 3P MCBs than DP, so there might be a reason for use 3P as "standard" but I don't see much reason for wiring that way.

Where you sometimes see a 3P breakers or switches series-wired is for DC systems to increase the breaking limit where there is no zero-crossing of AC current to help extinguish the arc, though that is something to check with the manufacturer that it is acceptable.

John- · Mar 21, 2021

I will be calling the manufacturer tomorrow and will check with them then. Just checking it wasn't anything obvious.

thank you all.

john

Darkwood · Mar 21, 2021

Rockingit said:
I think there’s so many variations on symbols for switches/isolators it’s hard to make that distinction?

The symbols we use in schematics are of a few international standards, recognising what the symbol is here is a circuit breaker with only overload protection and no magnetic trip, the partial box shape on the line designates overload protection, if it was accompanied by a dome shape then we would have a standard thermo/magnetic circuit breaker which we use as a standard to protect circuits across the industry. (like your standard mcb)
A switch isolator is a different symbol altogether and I suspect the schematic designer has limited understanding here of the correct symbols to use, the relevant standards here are either ANSI (American) or EIC which is mostly the rest of the world, but the differences are not that big.

I have to agree though, I have seen some very inventive versions of symbols and clearly incorrectly applied symbols in my time.

@John- All the information for that schematic should be included on the schematic or a ref' code/symbol should be attached with a key elsewhere to denote its ratings etc Q would be a recognised standard marker for this schematic device followed by a number to identify it against others in use so if its the primary device it would be Q1 and you schematic key would identify its ratings. Just looking at the fact it has been built up out of 3 single overload devices then boxed and no common switching link I thus conclude it has been drafted by someone who clearly doesn't know the standards or hasn't got the software to do a professional draft.

Another genset question

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