isolators

M cebee

regarding 'isolators' is it unacceptable to loop- in to another pole (to split the load)

thanks

mazthespark

M cebee wrote: »

regarding 'isolators' is it unacceptable to loop- in to another pole (to split the load)

thanks

do you mean using another pole in the same isolator? would you not just use a bigger isolator?.

2011

No that should not be done. First off both poles will not open or close at exactly the same time. This would mean that a single pole is making and breaking a larger load than it is designed to.

Secondly there is no way to be sure that the load is evenly split

2011

mazthespark wrote: »

do you mean using another pole in the same isolator? would you not just use a bigger isolator?.

Exactly

mazthespark

some isolators allow the replacement of there internal parts if replacing the enclosure is the difficulty. i agree with 2011 its never done and no way to guarantee equal load split.

M cebee

i was assuming the poles were already correctly rated

mazthespark

whats the reason for splitting across poles then?

M cebee

was just curious with regard to arcing,load etc.

instead afaik wiring 2 poles in series will reduce arcing

ilovesleep

I can ask here what is an isolator. i'm in my rented place for a week now and i have seen the word isolator on a switch but i dont know what it is.

mazthespark

an isolator is basically a switch or an means of disconnecting some thing from its supply

ilovesleep

Cool thanks. im clueless about these things. its on a switch outside the bathroom so its probably for the extracter fan in the bathroom.

2011

M cebee wrote: »

was just curious with regard to arcing,load etc.

instead afaik wiring 2 poles in series will reduce arcing

Connecting in series will not reduce arcing.

M cebee

thanks

think im drinking too much coffee

2011

M cebee wrote: »

thanks

think im drinking too much coffee

No problem. Good luck with it.

RoundyMooney

mazthespark wrote: »

whats the reason for splitting across poles then?

It's a bodge;)

AFAIK, isolators are designed to break the neutral last (talking in a domestic or small commercial sense here), so as said, you're banging all the load onto one pole, even if it is only for a very short period.

Of more importance, is that because of design tolerances, the current may not flow evenly across the pair anyway.

M cebee

i'm using 4-poles -they're well rated

thought maybe i saw the 2 spare poles utilised-could have been contactors:D

the RC snubber is used for arc suppression but the circuit may have to be designed according to the load being switched -not sure

RoundyMooney

Not sure

They're in series with the load, so shouldn't be current dependent.

2011

How big is this load in terms of amps or kW?

What type of load is it?

What is each pole of the isolator rated at?

AFAIK, isolators are designed to break the neutral last .

I never heard that before. Why would that be desirable?

I was told that AC isolators were designed to be "fast make" and "slow break".

M cebee

seem to have stirred up a hornets nest.

just regarding the standard 20,32 63 4-pole isolators i thought maybe i recalled somewhere seeing the load distributed over the 2 spare poles as well(for single -phase)-although i could be thinking of contactors
(assuming the poles were already correctly rated)


the DSO or ESBN will certainly be breaking neutrals last and making first anyhow(neutral inverson etc.)

4-pole isolators and rcds would prob need to break the neutral last i imagine-never looked in to it(unbalanced star connected loads)

on a 3-phase tn-c-s installaion afaik the the neutral shouldn't be switched at all except to isolate SP loads and for 4-pole rcds

RoundyMooney

I have seen it done on contactors alright

I'd imagine, as with the isolator, it will probably (almost definitely) work away fine, but wouldn't pass muster in an inspection scenario.

I'm not sure about the isolators built into the newer iskra meters-think they only break the phase, but the seperate ones almost certainly break both poles. I'll check tomorrow if I remember.

Neutral inversion is a slightly different problem mcebee, but you're quite right about the dangers of breaking a neutral before a phase, even if only for brief periods!

RoundyMooney

Here's one, which I won't obviously disclose the location of, but involved (on a customers side) a broken neutra on a supply l feeding a load in a seperate building.

This guy didn't even notice the problem, but his neighbour, who reported the issue did, when he went a-milking one morning, and all his cows keeled over-luckily I gathered they were all okay.

This guys wife was wondering why she was getting tickled while wiping down the cooker, and other neighbours experienced similiar symptoms as well.

M cebee

RoundyMooney wrote: »

I have seen it done on contactors alright

I'd imagine, as with the isolator, it will probably (almost definitely) work away fine, but wouldn't pass muster in an inspection scenario.

I'm not sure about the isolators built into the newer iskra meters-think they only break the phase, but the seperate ones almost certainly break both poles. I'll check tomorrow if I remember.

Neutral inversion is a slightly different problem mcebee, but you're quite right about the dangers of breaking a neutral before a phase, even if only for brief periods!

but if esbn break a neutral before a phase the consumers met will go live

ie:neutral inversion

RoundyMooney

That wouldn't be my understanding of what a neutral inversion is (but I'd welcome a definition if someone knows better:))

Neutral inversion to me is where a phase is inadvertently earthed, which has a similiar end result, in that you get a higher voltage on the blue wire, relative to earth.

2011

That wouldn't be my understanding of what a neutral inversion is (but I'd welcome a definition if someone knows better)

My understanding is that it is when the neutral is a a higher potential than the phase. With a neutralized installation the danger is that exposed metalwork would become live. This can happen when a large fault current flows up the earth rod of an other installation that is close.

seem to have stirred up a hornets nest.

Not at all. I am sure Roundymoney is correct. I just had not heard of this before. I had with an isolator for an entire installation, but not for one specific item such as this case.

M cebee

for the sparkie anyhow 'neutral inversion' would be a broken neutral on a tn-c-s supply

i may have been thinking of contactors

i believe series contacts have been used in arc supression but don't have any reference to it.

so is there any standard 'snubber' available off the shelf or integrated into
switches i wonder

RoundyMooney

You could well be right folks, the internets would seem to agree with you as well

In yellow van land, we always termed it as such when a phase was earthed inadvertently, which can happen on two wire systems! As you know, anything over two volts from neutral to reference earth is deemed outside standard, partly for this reason.

Anyway, getting back to the original topic, I can't help on the snubber I'm afraid, not my field at all.

Bruthal

RoundyMooney wrote: »

You could well be right folks, the internets would seem to agree with you as well

In yellow van land, we always termed it as such when a phase was earthed inadvertently, which can happen on two wire systems! As you know, anything over two volts from neutral to reference earth is deemed outside standard, partly for this reason.

Anyway, getting back to the original topic, I can't help on the snubber I'm afraid, not my field at all.

I never seen a broken neutral as neutral inversion myself for some reason. When the neutral is broken its no longer a neutral. I always thought of it as an intact neutral having a greater potential with reference to earth than the phase or phases due to a phase being accidently connected to earth. So in a vector diagram the neutral would not be in the centre. Too much drink im having again.....

M cebee

2011 wrote: »

Connecting in series will not reduce arcing.

http://www.schrackrelays.com/schrack/pdf/C0_v4bg_4.pdf

there's a reference on page 22 to wiring relay contacts in series to reduce arcing,although i think a 'snubber' is more common

in fairness paralleling isolator poles is prob pointless,i'm confused these days:D


rules 461.3 regarding isolator neutral poles-they can break after or make before line/phase poles

Bruthal

M cebee wrote: »

http://www.schrackrelays.com/schrack/pdf/C0_v4bg_4.pdf

there's a reference on page 22 to wiring relay contacts in series to reduce arcing,although i think a 'snubber' is more common

in fairness paralleling isolator poles is prob pointless,i'm confused these days:D

So am i, it must be an age thing with myself