3 or 4 pole

grousedogtom

Hi, I am fitting a change over switch on a 3 phase supply, the switch I got from the wholesaler is a 3 pole, by using this I won't be switching the neutral through the change over switch, should I be using a 4 pole switch to break the neutral also or what is the best practice? Many thanks

2011

grousedogtom wrote: »

Hi, I am fitting a change over switch on a 3 phase supply, the switch I got from the wholesaler is a 3 pole, by using this I won't be switching the neutral through the change over switch, should I be using a 4 pole switch to break the neutral also or what is the best practice? Many thanks

Personally I would like to use a 4 pole device.
Remember the neutral conductor is considered a "live" conductor.
Therefore a 4 pole switch will permit complete isolation from either the ESB supply or the generator and if it is a 3 position switch isolation from both.

Calgary22

4 Pole mate:D

grousedogtom

Ya, thanks people, 4 pole be safer, 4 pole it is

Irish Steve

Interesting.

A good while back, I put a 3 phase semi-automatic change over system in using interlocking contactors, and to avoid a floating Neutral when nothing was connected, ESB required me to tie all the neutrals together so that there was a valid connector for the contactors to work correctly during changeover. They picked it up when the planned circuits were submitted for approval before installation, it was a LONG time ago , back in the days when the local ESB office controlled what went on in their area, and came out themselves to inspect it before accepting it into use.

It's been upgraded since then, and is now fully automatic, and self start and shut down, but the original generator was petrol engined (nightmare of a thing, and cost a ransom to run) so needed time to warm up, and care with the choke during that time, so contactors were used to allow for switching once the supply was stable, and manual switching was not an option due to the way the supplies work.

I was under the impression from the discussions at the time that the Neutral is earthed either at the mini pillar or back at the local transformer, but that may not be the case now, not sure.

2011

Irish Steve wrote: »

Interesting.

A good while back, I put a 3 phase semi-automatic change over system in using interlocking contactors, and to avoid a floating Neutral when nothing was connected, ESB required me to tie all the neutrals together so that there was a valid connector for the contactors to work correctly during changeover. They picked it up when the planned circuits were submitted for approval before installation, it was a LONG time ago , back in the days when the local ESB office controlled what went on in their area, and came out themselves to inspect it before accepting it into use.

It's been upgraded since then, and is now fully automatic, and self start and shut down, but the original generator was petrol engined (nightmare of a thing, and cost a ransom to run) so needed time to warm up, and care with the choke during that time, so contactors were used to allow for switching once the supply was stable, and manual switching was not an option due to the way the supplies work.

I was under the impression from the discussions at the time that the Neutral is earthed either at the mini pillar or back at the local transformer, but that may not be the case now, not sure.

Following your reply I have had a look at the three 2MVA stanby generators we have on site. When we use these in "island mode" to supply the site the 3 phases and neutral are disconnected from the ESB supply.

I met with a member of the ETCI council today and discussed this matter. His position was that if the neutral was left connected to the ESB then a neutral current could inadvertently be exported to the network.

Interstingly also discussed was that when the ESB supplies our site the NER (neutral earth resistor) is connected in circuit to limit potential fault current to ensure that it is below that of breaking capacity of our switch gear. When the generator supplies the load in island mode (without the ESB in parallel) this resistor is switched out of circuit as the maximum fault current is limited by the generators themselves.

Bruthal

2011 wrote: »

I met with a member of the ETCI council today and discussed this matter. His position was that if the neutral was left connected to the ESB then a neutral current could inadvertently be exported to the network.

It would be interesting to hear his theory on that one.

2011

Bruthal wrote: »

It would be interesting to hear his theory on that one.

I will see him in the next few days and will ask him and let you know.
PM sent.

liveandnetural

bumped...... just to see was there outcome from 2011