400v sauna heater

christramp

I've recently moved my sauna in from an outside building into the house. It's a 4500 watt unit and states it's 400v 3N. I had it fed from the main board off a 63amp rcd into a spur unit holding a 63amp rcd and fed into a 40amp circuit breaker which fed the sauna and a 16 amp breaker that fed sockets. This ran fine for two years. It was running on 10 square cable.
I moved it inside and ran the same arrangement but the cable length is considerably shorter. 12 metres down to 5 metres. The rcd keeps tripping after 5 minutes when the heater starts warming up to it's temperature.
I've taken out the rcd at The spur in case the two rcds were fighting each other and just fed it into the 40 amp breaker but the same result happens.
I could just put a straight connection back to the board on a 50 amp breaker but I'd be happier having the rcd.
I've been told it's possible it's a 3 phase unit looking to draw 400v from a 240v single phase supply but why has it ran for two years with no issues.
I'd appreciate any advice you can give
Cheers
Chris

M cebee

Not familiar with saunas

i assume the elements are star connected and it can run either 230 or400
you dont need two rcds in series but there could be a heater fault
dont remove them

2011

christramp wrote: »

It's a 4500 watt unit and states it's 400v 3N.

Ok, this is small enough a load for a single phase supply to manage.

I had it fed from the main board off a 63amp rcd into a spur unit holding a 63amp rcd and fed into a 40amp circuit breaker which fed the sauna and a 16 amp breaker that fed sockets.

It would be best for it to have a dedicated RCD. 40A MCB is too large for this load. Current drawn should in the region of 20A.

This ran fine for two years. It was running on 10 square cable. The rcd keeps tripping after 5 minutes when the heater starts warming up to it's temperature.

The cable size sounds good.
Think of how an RCD works: if the current going out on the live is not equal to the current returning on the neutral then it will operate. You have a fault to earth or an RCD is connected incorrectly, or a faulty RCD. I would guess it is the former. Cables or the element may be damaged. Try a meggar test on the unit when disconnected. Also do the same with the wiring.

I've taken out the rcd at The spur in case the two rcds were fighting each other

This dose not make sense. RCDs do not "fight" each other. They can be installed in series although it would generally be pointless.

I could just put a straight connection back to the board on a 50 amp breaker but I'd be happier having the rcd.

Against regulations and not safe. I would use a 25A RCBO if I was doing this.

2011

Electricity + water heater of this kind requires dedicated RCD protection.

antoinolachtnai

Just a thought - one of the heating elements could have been damaged when you moved it. You might have to replace an element. I am no expert, but if too much cold water hits those elements when they are hot, it can weaken them.

I suppose the thing to do here would be to test the heating elements individually and if it doesn't make the fault obvious, then run the heating elements individually and see if you can find out which one is causing the problem.

christramp

antoinolachtnai wrote: »

Just a thought - one of the heating elements could have been damaged when you moved it. You might have to replace an element. I am no expert, but if too much cold water hits those elements when they are hot, it can weaken them.

I suppose the thing to do here would be to test the heating elements individually and if it doesn't make the fault obvious, then run the heating elements individually and see if you can find out which one is causing the problem.

I have just replaced one of the elements as it would not heat. Ive tested all of the elements for continuity and also heated each of them individually I'm going to try and look at changing the breakers as previously suggested

christramp

2011 wrote: »

christramp wrote: »

It's a 4500 watt unit and states it's 400v 3N.

Ok, this is small enough a load for a single phase supply to manage.

I had it fed from the main board off a 63amp rcd into a spur unit holding a 63amp rcd and fed into a 40amp circuit breaker which fed the sauna and a 16 amp breaker that fed sockets.

It would be best for it to have a dedicated RCD. 40A MCB is too large for this load. Current drawn should in the region of 20A.

This ran fine for two years. It was running on 10 square cable. The rcd keeps tripping after 5 minutes when the heater starts warming up to it's temperature.

The cable size sounds good.
Think of how an RCD works: if the current going out on the live is not equal to the current returning on the neutral then it will operate. You have a fault to earth or an RCD is connected incorrectly, or a faulty RCD. I would guess it is the former. Cables or the element may be damaged. Try a meggar test on the unit when disconnected. Also do the same with the wiring.

I've taken out the rcd at The spur in case the two rcds were fighting each other

This dose not make sense. RCDs do not "fight" each other. They can be installed in series although it would generally be pointless.

I could just put a straight connection back to the board on a 50 amp breaker but I'd be happier having the rcd.

Against regulations and not safe. I would use a 25A RCBO if I was doing this.

Hi
Thats great, it all makes sense. I'll change down the rcbo and breaker and I'll check the cable and earth again. If all of this does not work it will be down to the two remaining old elements and I'll test them out again.
Thanks for the advice

2011

christramp wrote: »

Hi
Thats great, it all makes sense. I'll change down the rcbo and breaker and I'll check the cable and earth again. If all of this does not work it will be down to the two remaining old elements and I'll test them out again.
Thanks for the advice

Good luck with it. Let us know how you get on.

christramp

I changed down all of the breakers and still no joy - tested the elements again and nothing - Then went and checked the cable inch by inch and found a snag where the earth was cut - guess what - all working fine now.
Cheers guys - just goes to show it can be the simplest of things sometimes

slattsteen

anyone know where id get replacement infra red ceramic heaters