Head scratcher for trainees, and others

[littlespark]

I was asked to look at a storage heater that wasn't working.

Set up is a combined double row MEM board with lighting and power on top row, and 3 way split row on the bottom for water heating, storage heaters and panel heaters, each with their own double pole mainswitch and neutral bars.
A couple of storage heater points have been changed to the panel heater side for different heaters.

The problem was a faulty 20A double pole switch for the storage heater in question.

Now, for the quiz.
Having turned off the mainswitch for all the storage heaters, but not the panel heater side, and the timeclock not turned on, I was getting 230v between neutral and cpc at my switch. WHY?

I was not getting power between live and cpc, or live and neutral.... only neutral - cpc

Suggest answers in your replies.

 

[buzzlightyear]

answer for that was the neutral still had current to it a borrowed neutral.or live was down the neutral.

 

[littlespark]

There isn't a L-N swap.
The clue is with the points being changed from off peak to 24hr

Give any trainees a chance

 

[Lister1987]

I would've hazarded a guess at a shared neutral from an energised circuit? Sharing say from the lighting circuit so even when the heater circuit was isolated, it was still getting power from the live lighting circuit?

It's the only way I can see it, getting power from a different source? Not done a lot of borrowed cables so my understanding may be off?

 

[GBDamo]

Are all the neutral bars in the CU discrete?

One or more of the live circuits terminated to the wrong N bar.

 

[James]

I am thinking shared neutral, possible from the time clock motor?

 

[littlespark]

Yes, the neutrals were the problem.

Whoever moved 2 of the storage heater points onto the 24hr side only moved the lives, and not the neutrals.
Everything worked as it should, but when I turned off the offpeak mainswitch, the 2 circuits that had been moved no longer had a return path.

So an hours fault finding and switch replacement turned into a 3 hour job.

"it was an electrician that did that!" pronounced the customer.
Yes... the same electrician that didn't mark up the board whatsoever

 

[GBDamo]

Yes, the neutrals were the problem.

Whoever moved 2 of the storage heater points onto the 24hr side only moved the lives, and not the neutrals.
Everything worked as it should, but when I turned off the offpeak mainswitch, the 2 circuits that had been moved no longer had a return path.

So an hours fault finding and switch replacement turned into a 3 hour job.

"it was an electrician that did that!" pronounced the customer.
Yes... the same electrician that didn't mark up the board whatsoever

Do i get a prize?