3 phase over door heater switch connections

[Guest 004]

Went to a job today, and was asked by the builder to re connect a 3 phase over door heater switch, which had been disconnected by others.

The switch in question is a 4 gang switch, and only has 1 phase, so I am at a bit of loss of the connections, as there is only 1 phase at the switch, and 5 single red cables, and an earth?

My first thoughts were maybe that the blower motor that is built into heater had 4 speed settings?

so 1 feed, 4 switch lines, but as I did not have access equipment to get the heating connections, I politely refused.

Any thoughts anyone??

IQ where are you

 

[Des 56]

A scenario I have seen in the past
Would it be an installed original 3 phase heater where only single phase was available
The elements connected in star with 3 seperate single phase supplies to each element and a common neutral

 

[Guest 004]

The supply comes from a 3 phase MCB

 

[GOODWIN]

so theres a 3phase supply to the motor and this is the switch connections (the single phase is prob linked off one of the 3 phases from above, from the supply side with a/should have fuse to down rate it before the switching stuff)

 

[Guest 004]

I was thinking maybe one element per phase/switch, but that does not explain just one phase at the switch and 5 cables

 

[nickblake]

It Depends on the heater make , what has been done in the past was 12kw door heater 3 phase , 1 phase per elemnet , but also uses one of the single phases for the motor and control circuits so basically you have a 230 volt motor controlling the air flow motor hence the single phase switch bank , these also control a section of relays which switched the heating elements on via the switch bank again single phase , i have some where im the dleves of my office a drawing for one of these heaters , but i may have thrown it make of the heater would be an idea , so single phase for the control circuits switching 3 phase for the elements

 

[Guest 004]

yep that sounds more like it, so if i just looped the live, and had 4 switch lines, could i try you think? it seems quite old

 

[nickblake]

the one i have wired have done just that common then 4 switch wires give it a try , its a while since ive worked on one so my memory's a little vague but inside the heater ther should be the switch connections into a terminal block i know they used to lable them L1L2L3L4 etc but they may have changed this when the regs changed the phase name from Y1R1B1 etc , let us know how you get on be good to refresh

 

[Guest 004]

will do, and thanks