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Water heater. Correct cable to use
Baldyhugh 11001211038
Joined 08/05/2019 - 38 Posts
Hi all

I have a large 6kw water heater to connect at a farm for washing a bulk milk storage tank. It is made made by Cotswold heaters and consists of a large insulated tank inside an outer steel box. It is controlled by separate control box containing timers and a contactor and connections for solenoids and a float switch. In the heater itself it is prewired to some din rail mounted style connectors to then accept the incoming cables. The prewired cables from the block to the heater terminals are heat resistant and the other smaller cables to the solenoid and float switch appear to be so aswell. My question is should the incoming cables be heat resistant as they don’t connect directly to the heater element terminals. If it was just a standard heater I would use a single heat resistant flex but there are control cables aswell with just a single cable entry to the heater so I was going to use flexible conduit and singles from the control box to the heater. I have wired a few of these before this way and the cables have been ok years later but in the spirit of bettering my methods I was wondering what way others would attack this job. Would some heat resistant sleeving over the singles at the heater End suffice or where should the requirement for heat resistant cables begin and end? See picture of heheater, sorry about the quality. The heater is at the bottom and connections are all behind the clear Perspex cover, hopefully the picture explains what I’m on about
8 Replies
mapj1 80733779
Joined 22/07/2004 - 1901 Posts
That grey terminal strip is nothing special in terms of temp rating, so long as you are on the non-heater side of it, PVC will be fine. By all means over-sleeve for identification and peace of mind, but it will not cook the cables without cooking those  terminals first.
Baldyhugh 11001211038
Joined 08/05/2019 - 38 Posts

Thanks KFH and others. See picture of heater, hopefully it explains a bit better what I’m on about. I’ll probably end up using singles as I have used this method previously without problems. Thanks for your input.
whjohnson 11001209847
Joined 21/02/2019 - 285 Posts
You could go down the tri-rated route if you wished to over-egg the pudding though.
kfh 1100191327
Joined 17/02/2015 - 99 Posts
I maintain a similer boiler for a farmer. It must be at least 30 years old and I did not install it. 

None of the supply cables are heat resistant. With the exception of the supply to the heater none of the internal cables are heat resistant and some have been replaced over the years when contractors or thermostats have been replaced with different items with different wiring configurations. None are showing any heat damage. 

As the maximum water temp used will be about 80 - 90 degrees and the tank is insulated, the temp in the connection/controller box should never get near this and I doubt any of the components around the connections are rated at more than 70 degrees. As the manufacturers instructions make no reference to using heat resistant cable or sheathing, I would not worry about using standard cable.

Baldyhugh 11001211038
Joined 08/05/2019 - 38 Posts
That’s the one. I’m on site today so I’ll get a close up picture of the the connections and try to post it
OlympusMons 11001209648
Joined 09/02/2019 - 85 Posts
Baldyhugh 11001211038
Joined 08/05/2019 - 38 Posts
Sorry I thought I had attached the image but it mustn’t have worked. It wasn’t very good quality anyway. The manufacturers instructions don’t specify unfortunately
-2400- 11001209207
Joined 15/01/2019 - 60 Posts
Hi, not sure if it is just me but I can't see any attachment or image?
I might as well ask the obvious question as well - what if anything do the Manufacturer's Instruction say?

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