Wiring help for 230/240V circuit breaker in UK

[biltrite33]

I'm an American trying to help a friend in the UK hook up a branch circuit. He received several 2 pole breakers for this task and wants to know how to connect his feeders to the RCD. Now in US our 220V lines use a 2 pole breaker and 3 wires (2 "HOT" black lines connected to individual phases of 120V each to get 220V single phase. The third wire is the ground.) The problem I've come across is that he speaks of his 230/240V being 3 wire 1 "hot", 1 "neutral", and 1 "ground" which leads me to believe that his circuit should be connected similar to the 120V single phase circuits in the US, where one hot goes to a single pole breaker and depending on whether you are connecting the branch circuit in a main or sub panel if the neutral gets "BONDED" to ground or not (neutrals bonded to ground at the main panel and has a seperate bus in a subpanel). I just want to confirm if this is the case before I give him misleading info because I told him in the US we try to avoid switching the neutral. PS the breakers he showed me pictures of are similar to a 2 pole breaker you would see used to replace a fuse block in a control cabinet for machinery. He told me thats what they use in their houses in UK.

 

[rbulsara]

If it is a 230V or 240V Line to Neutral single phase feed, he/she has to use a single pole breaker. If he must use 2-pole breaker, then just use one pole and other pole will be unused.

MY questions is: Can his/her panelboard accept a 2-pole breaker? If he does not have second phase, where would the second pole of the breaker will tie to?

 

[biltrite33]

The way he described it and the pictuce of the breakers he showed me show screw terminations for incoming feeders and screw terminations for line connections. These breakers are din rail mounted NOT on a bus like, for example, a Square D or GE main panel. They are similar to a fuse block in a machine control panel and would be used in place of a fuse block in said panel. And it isn't a panelboard either more like the fiberglass trough boxes. Actually the box looks rather like a manual motor starter enclosure

 

[ScottyUK]

biltrite,

The UK breaker is a standard European design. They have dual mounting options: either clip to DIN rail for stand-alone use within a panel; or mount into a pan assembly with a busbar structure (1-ph or 3-ph) onto which the breaker mounts. The terminal screws operate a rising clamp arrangement which can accomodate either a cable or lug, or clamp onto the tongue of the busbar. US designs seem to use a sprung clip on the busbar side IIRC.

Unless he is using a 415V 1-ph system connected line-line, in which case he would need a 2-pole breaker, he should use a single pole breaker. The neutral conductor must be tied to the neutral bus within the panelboard. Any switching of the neutral must be achieved using a ganged switch which simultaneously opens the line and neutral paths. On the whole, arrangements requiring this switching method are relatively uncommon.

The only reason you would have something resembling a 2-pole breaker in a domestic installation would be it it is a RCD, RCBO, or main switch. Almost all of these have the same form factor as a 2-pole breaker, although there are a few RCD / RCBO designs which only occupy a single pole.

The breakers he has received: does he know if they are Type B, C, or D? Will they meet the required disconnection time for the circuit in question? There are published maximum loop impedances for each type of breaker; a long circuit or one with marginally sized conductors can cause problems.

You friend may wish to investigate the restrictions under Pat 'P' of the Building Regulations regarding what he is permitted to do as a layman.

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