Single phase spur from Three phase isolator.

[fatboyslim]

Morning all,

Little advice regarding whether spuring from a Three phase isolator to a single phase FCU is allowed?

I need to wire a Single phase FCU which is located right next to a 16A TP isolator to a high speed door. Obviously, It would be a lot less pain to wire straight from the TP isolator to a SP FCU. Rather than running a cable from the Sub main for the FCU.

Anyone have any objections? I know it's not ideal. However, via a regulations point of view I can't find anything against this practice.

Cheers.

 

[littlespark]

the TP circuit will have been designed for the size of load across the 3 phases for that piece of equipment....

to then add a SP load off one of the phases at that point may overload that one line out of the three.

 

[fatboyslim]

the TP circuit will have been designed for the size of load across the 3 phases for that piece of equipment....

to then add a SP load off one of the phases at that point may overload that one line out of the three.

TP circuit is fed from a C16 MCB with the FLC of the high speed door at 6A/phase. The SP FCU will power a security roller door which has a FLC of 6.5A. Realistically both doors cannot be used at the same time as the security roller door must be opened first before the high speed door will operate.

Hope that makes sense.

 

[Rockingit]

Think about it this way: if you had a 3Ph supply running to a small 3Ph DB which had a 3P MCB in it feeding an occasional device and the DB had 3 x 1P slots available, would you be posting the question?

 

[DefyG]

Funnily enough I was on a job the other day where they had 2 roller shutter doors (3ph) on the same 10A supply, one effectively 'spurred' off the other.
Circuit cabling 2.5 so never going to be overloaded and whilst not sure of the flc, overloading of the mcb wasn't an issue the mcb had not been reported as tripping (it wasn't what I was on site for).
So no not ideal but no objections, its just another radial circuit!

 

[mickegh]

I would say it's a somewhat unacceptable practice

It may be undesirable for example for a fault to take out both doors

 

[westward10]

I really can't see a problem with it assuming there is a neutral there.