Replacing storage heaters with panel heaters

[kingeri]

Got a job coming up replacing 3 old storage heaters with panel heaters. Customer is coming off E7. Had a look today and was expecting the usual 3 x 16A MCBs, but found that all 3 heaters are on a single 6mm^2 circuit. There is an 850W unit, a 2.55kW and a 3.4kW one sitting on a 32A MCB. I have never seen storage heaters installed like this. If nothing else, loads greater than 2kW should be on dedicated circuits. The loading of the panel heaters is going to be similar, 29A ish, although the load won't as punishing due to cycling on and off and not all being on continuously for hours. I haven't decided if I am happy to do the change with this circuit as it is. Mind you I haven't tested the cable yet either. Any advice or thoughts would be appreciated.

 

[Deleted member 9648]

Would depend on volt drop calculation being OK and terminating 2x 6.0mm cables in a 13a FCU. Otherwise despite being unconventional I would have thought it OK. Clearly the 3.4kw storage heater should not be on a 13a FCU nor a 20a dp switch as it would then be fused at 32a. but as long as your panel heaters can be on 13a FCU's....

 

[kingeri]

Yeah thanks for that. I think volt drop will be fine as the circuit isn't overly long. Probably just over thinking. Which at least is better than under thinking! Looked like a JB arrangement so fingers crossed only one cable per FCU.

 

[Dozer 73]

A bit of food for thought for you and customer , put time clock, thermostat and contractor in
You should get a more controlled heat , also save the customer a fortune in the long run , in fact some of these modern heaters also have pir’s in them so if no one in the room it turns off or down to a set temp for eco or boost etc

 

[123]

A bit of food for thought for you and customer , put time clock, thermostat and contractor in
You should get a more controlled heat , also save the customer a fortune in the long run , in fact some of these modern heaters also have pir’s in them so if no one in the room it turns off or down to a set temp for eco or boost etc

Can get heaters with Clock and Thermostat built in which would be better as heating is zoned.

 

[Ian1981]

Install a 20 amp double pole switch for the 3.4kw heater and wire the heater in 2.5mm heat resistant flex as a 2.5 3 core flex will have adequate fault protection on a 32 amp type b or c mcb at 6ka.(think a 2.5 spur from a ring protected by a 32amp mcb and there will be no overload protection requirement for the heater)
Hager anyway give an I2t let thorough energy at 18ka for disconnection times under 0.1 seconds (other manufacturers may give slightly different values tho)so gives a minimum 1.5mm size for compliance

 

[westward10]

Not sure any manufacturer of 20A switches suggest 12mm of conductor to be connected at their terminals, or FCUs come to that??

 

[Ian1981]

Not sure any manufacturer of 20A switches suggest 12mm of conductor to be connected at their terminals, or FCUs come to that??

Give the 6mm a hair cut

 

[Dozer 73]

Can get heaters with Clock and Thermostat built in which would be better as heating is zoned.

We fit a lot of electric heating in temp buildings and relying on stat built into the heater just doesn’t seem accurate and we find the heater it self lasts a lot longer when an external stat is controlling all the switching , if you fit a stat central it will work like conventional heating system and give an average reading if you place the stat in the correct position
But suppose all depends on quality of the heater , where does it mention zoned heating in thread ?

 

[Dozer 73]

We fit a lot of electric heating in temp buildings and relying on stat built into the heater just doesn’t seem accurate and we find the heater it self lasts a lot longer when an external stat is controlling all the switching , if you fit a stat central it will work like conventional heating system and give an average reading if you place the stat in the correct position
But suppose all depends on quality of the heater , where does it mention zoned heating in thread ?

I think I have side tracked from the original question

 

[kingeri]

Install a 20 amp double pole switch for the 3.4kw heater and wire the heater in 2.5mm heat resistant flex as a 2.5 3 core flex will have adequate fault protection on a 32 amp type b or c mcb at 6ka.(think a 2.5 spur from a ring protected by a 32amp mcb and there will be no overload protection requirement for the heater)
Hager anyway give an I2t let thorough energy at 18ka for disconnection times under 0.1 seconds (other manufacturers may give slightly different values tho)so gives a minimum 1.5mm size for compliance

Thanks but the ratings I gave were for the existing storage heaters. The new ones I think will be 2 x 2kW and 1 x 3kW.

 

[kingeri]

So I am here at this job now and I wondered if anyone can answer this. Attempting to replace a carp taped up joint that I found under the floorboards with a MF alternative. 3 x 6mm^2 T&E to be jointed. Got a Wagobox and was going to use 3 x 773-173 connectors, as they will take up to 6mm stranded as well as the 2.5mm CPCs, and are rated at 32A when used MF. Snag is, the Wagobox will only physically take 2 of these. So I have used 2 of them for line and neutral and a 773-104 for the CPCs. This is rated at 20A when used MF. Does this sound okay?

 

[Ian1981]

Considering the cpc is designed to take fault current only up to a fraction of a second or 0.4 seconds max in this instance I would say this is fine if they are connected in a 20 amp rated joint.
Most fault currents are plus 100 amps anyway on a low enough zs and considering a b type 32 amp mcb needs at least 3-5x 32 amps to trip between 0.1-5 seconds.

What’s the arrangement?
Is it a single 6mm from the db then 2x 6mm feeding a heater each from the single 6mm?

 

[kingeri]

Cheers Ian for the reassurance. The 6mm goes from the CU to a JB under the living room floor where it splits to feed the 3kW heater, then carries on upstairs where it splits to feed the 2 x 2kW heaters. Managed to get that joint in a back box with blanking plate but used Wagos again.

 

[123]

It's not of much help now, but the Wagobox XL would take 3 6mm T&E cables and more.