Connecting backup generators to existing electrical installation

[Kevin Stubbs]

When connecting a generator to the electrical board of my house ,do I have to install cross over switches on the neutral and earth as well

[Dave A]

When connecting a generator to the electrical board of my house ,do I have to install cross over switches on the neutral and earth as well

Certainly not on the earth. It would be a bastard to seperate anyway unless you were crossing over the entire installation.

I don't see much need to isolate the neutral* - the allowed potential between earth and neutral is so low anyway, but then some electrical appliances need to have isolators (live and neutral disconnect)

Hopefully a more definitive answer will be forthcoming shortly.

*I'm just a director of an electrical contracting company - but not an electrician.

[Dave A]

Hmm. I've been looking at our wiring diagram (we're using an interlocked contactor rig) and thinking about this. You certainly want the neutral between the generator and the crossover switch isolated when you're on mains power. Which means yes, run the neutral through the cross-over switch.

Whilst I'm about it, I read an article this morning where the ECA had commented on generators. A few points from that:

• A COC has to be issued when wiring a generator into an existing installation that also has mains supply.
• There has been one death by electrocution by a generator in Durban already. (I see the main problem being they don't have earth leakage units.)
• The "plug generator into a plug point to power your house" is very dangerous.

I think I'm going to get my guys to point out to me anything in the SANS electrical installations code to do with generators. Murdock mentioned there was very little in a previous post. This could be interesting.

[Dave A]

I've just run through this neutral issue with my guys. In brief:

On a single phase installation, just like the live line has to be seperated from the main supply whilst under generator power, exactly the same with the neutral.

On a 3 phase installation being powered by a 3 phase generator, the neutral does not need to be isolated from the main supply.

If you are energising just one phase with a generator on a three phase installation, you need to treat that part of the installation as a single phase supply. Thus you'll also need a mechanical isolator to that part of the installation as well as the cross-over switch.

[topak]

gee..i want to learn more about Martinez Electric installation

[murdock]

and just to put a spanner in the works....no matter what the code says...you have to abide by the local supply authourity requirements and i am told that in durban you have to use a 4 pole transfer switch as required by them (yet to get some formal document as i am sure you will understand why)

[murdock]

there is now a section 7:12 which covers generators and other alternative supplies...boy does it get interesting when you read it...what blows my mind are the variety of responses from people including generator suppliers and installers...

this section covers this topic quite well...and if not read properly can be a bit misleading.

[Dave A]

Los Angeles is a whole different world away from South Africa, Topak.

Aren't you guys on 110V in those parts.

[murdock]

a single phase and three phase supply must isolate the neutral... the changeover contact must be a 2 pole for single phase and a 3 phase must be a 4 pole.

the installation must be done by a qualified electrician...who knows and understands generator supplies...lots of electricians i have come acroos recently dont have enough experience to advise or install generators

beware south africa and america have different volatages earthing systems ie TT...TNC...TNC-S etc and the voltages are diffferent... we have phase to neutral 240 whereas they have phases to phase 240 volts...and 120 volts...60 hz not 50 hz...our electricity supply must not be compared in any way...if you do want to compare it must be with uk and australia.

most generator installation which i have come across are illegal but they work so the customer is not prepared to spend the money to make it right...they say why fix something that works.

i found a changeover other day where they using a contactor as a changeover switch the n/c contact is the generator supply...the n/o...n/c contacts of a contactor are not rated to 30 amps

but unfortunately until they start impossing heavy fines for illegal work the public will be the ones who suffer...and in saying that the public are half the problem because they the ones who are using the unregistered companies...because they are.............yes that is correct.... CHEAPER...in these difficult times who blames them.

[Dave A]

i found a changeover other day where they using a contactor as a changeover switch...

Murdock, given that the changeover must be mechanically and electrically interlocked, how can this be achieved without contactors?