400v single phase heating element

normally a resistive heater designed for 400V would be strung between a pair of phases. There is very little merit in stepping up to create a new supply of 400V L-N from a 230/400 supply.

690 phase to phase, so  400V to ground/neutral exists in the UK as an industrial standard, normally when the site has its own substation and uses things like cranes on rails that run the full length of a big hanger so the  voltage drop over distance is an issue. 

It is quite rare, the switchgear is quite expensive, and at the very least "caution 690V 3 phase" should be very clearly marked as such and segregated from the normal wiring.

It is however just the next logical voltage click up from 230/400 to go to 400/690.

It is useful if you have a lot of power to go a long way, but its not what is normally expected in the UK. 

On a related note, even higher voltages are possible, I have, but only in a massive factory in Germany, also seen 690/1k2 - with 690V to earth/neutral and 1200V between phases. It impressive how many KVA can be sent so far on a set of cables so thin ;-) 

I'm not sure of the regulatory position if that were done in the UK as it is above LV, while 400/690 certainly remains under normal BS7671 LV type rules, albeit the next voltage column over in the tables for ADS etc.

In your case I'd suggest unless you have your own substation, or the power is many tens of KVA, stick to 230/400 and wire the 400V elements as a 3 phase delta.

Mike.

normally a resistive heater designed for 400V would be strung between a pair of phases. There is very little merit in stepping up to create a new supply of 400V L-N from a 230/400 supply.

690 phase to phase, so  400V to ground/neutral exists in the UK as an industrial standard, normally when the site has its own substation and uses things like cranes on rails that run the full length of a big hanger so the  voltage drop over distance is an issue. 

It is quite rare, the switchgear is quite expensive, and at the very least "caution 690V 3 phase" should be very clearly marked as such and segregated from the normal wiring.

It is however just the next logical voltage click up from 230/400 to go to 400/690.

It is useful if you have a lot of power to go a long way, but its not what is normally expected in the UK. 

On a related note, even higher voltages are possible, I have, but only in a massive factory in Germany, also seen 690/1k2 - with 690V to earth/neutral and 1200V between phases. It impressive how many KVA can be sent so far on a set of cables so thin ;-) 

I'm not sure of the regulatory position if that were done in the UK as it is above LV, while 400/690 certainly remains under normal BS7671 LV type rules, albeit the next voltage column over in the tables for ADS etc.

In your case I'd suggest unless you have your own substation, or the power is many tens of KVA, stick to 230/400 and wire the 400V elements as a 3 phase delta.

Mike.