2x 3kw immersions connected to 1 double pole switch and 16A MCB

[accessgas]

Hi, I was called to a job today where the property had no hot water, the double pole switch would not switch, I removed the face plate and could see the neutral wire burnt out. I have replaced the switch with a new one.

The double pole switch feeds a Quartz E7 timer which switched between peak and off peak so you never have both immersions on at he same time but someone has connected the boost live to the mains live and left the off peak connection where its supposed to be, this means during certain times of the day (between 02.00 and 08.00) both of the immersion are live and if the thermostats are calling for heat then both immersions will be drawing current. would this be the reason the double pole switch burnt out?

I have removed the boost connection from mains live and reconnected it back to the boost terminal

I'm just trying to explain the situation to the customer.

 

[JohnW2]

.... this means during certain times of the day (between 02.00 and 08.00) both of the immersion are live and if the thermostats are calling for heat then both immersions will be drawing current. would this be the reason the double pole switch burnt out?

If the switch and/or cable was rated at appreciable less than about 26A, then I imagine that the answer could well be 'yes'. Mind you, a B16 MCB should trip in well under an hour at such a load.

Kind Regards, John

 

[accessgas]

so the switch was labelled water heater I assume its a 20A switch. The supply cables to the switch are 2.5mm I think, the neutral cable was burnt out. I have never seen 2 immersions connected to the same switch or same MCB its not normal practice is it? the customer wants to know if this could have caused a fire?

 

[JohnW2]

so the switch was labelled water heater I assume its a 20A switch. The supply cables to the switch are 2.5mm I think, the neutral cable was burnt out. I have never seen 2 immersions connected to the same switch or same MCB its not normal practice is it?

It's obviously no acceptable to have two immersions (that could be 'on' at the same time) fed via the same 20a switch or from a circuit with a 16A MCB. Even 2.5mm cable would be marginal (and inadequate with all but the most generous of installation methods).

... by the the customer wants to know if this could have caused a fire?

Yep, I would imagine it could have.

Kind Regards, John

 

[accessgas]

Thank you for your advice. Have a good night.

 

[JohnW2]

Thank you for your advice. Have a good night.

You're welcome - and you.

Kind Regards, John

 

[Taylortwocities]

The Quartz E7 is designed so that the boost function does not work during the OFF peak period when the bottom immersion is already energised. So you could not have both immersions on at the same time.
You are right to correct the wiring.
if you don't have a manual, a copy can be found at http://www.free-instruction-manuals.com/pdf/pa_457948.pdf

 

[JohnW2]

The Quartz E7 is designed so that the boost function does not work during the OFF peak period when the bottom immersion is already energised. So you could not have both immersions on at the same time.

As I understand it, that's what the OP was describing, but that someone had circumnavigated that (sensible) functionality by connecting the boost immersion to the incoming L to the Quartz E7 - or did I misunderstand?

As you say, it is good that he has now corrected the wiring.

Kind Regards, John