Wiring supply in top of Isolators RCDS and mcbs

[Mikegh]

When shouldn't this be done ?

 

[littlespark]

When it goes against the manufacturers instructions???

Is this a theoretical question, or have you come across it on a job?

Isolators, it probably doesn’t matter as it’s just a switch… but mcbs and RCDs it will

 

[James]

Fused isolators, especially bolted tag type fuses.
they have a specific feed side and load side.
if you get it the wrong way round the fuses remain live when the isolator is switched off.

 

[pc1966]

if you get it the wrong way round the fuses remain live when the isolator is switched off.

One reason I like the Schneider "Quadbreak" style of fused-switch is they isolate both sides of the fuse, so you can feed either way and don't have to worry if the load is UPS-y and leaks a lot even with the supply disconnected (i.e. potentially both sides are "live").

MCBs probably not an issue.

Some RCDs can have trouble if powered from the load-side as stuff like test button is not disconnected when they fire and so can burn out. However, many RCD are OK from either end but it can be hard to get a definitive statement on that.

 

[Mikegh]

That's what I was thinking, standard isolators and mcbs ok thanks

 

[Mikegh]

When it goes against the manufacturers instructions???

Is this a theoretical question, or have you come across it on a job?

Isolators, it probably doesn’t matter as it’s just a switch… but mcbs and RCDs it will

Why do you say mcbs it will ?

 

[Marvo]

As above, according to manufacturers instructions. Where I am domestic and commercial CU's / distribution boards are almost always wired with supply on top and final circuits on the botton of circuit breakers / RCD's.

 

[Flanders]

When I spoke to hager tech about this they said that mcbs must be fitted the correct away round as I remember it ,it was to do with the direction the arc traveled in the event of a fault or overload

 

[LewisM]

When I spoke to hager tech about this they said that mcbs must be fitted the correct away round as I remember it ,it was to do with the direction the arc traveled in the event of a fault or overload

I’ve been told the exact opposite from Hager technical support, direction doesn’t matter and doesn’t effect operation at all.

 

[littlespark]

The MI tell you which end to connect to the busbar, and which end goes to the outgoing circuit. Whether it might work or not, you still need to follow the MI

 

[pc1966]

When I spoke to hager tech about this they said that mcbs must be fitted the correct away round as I remember it ,it was to do with the direction the arc traveled in the event of a fault or overload

When fitted to a DB/CU yes, but that is to do with the mechanical arrangement and possible results of arc gasses on the cables, etc. Not electrics as such. Also some MCB do not have identical clamps on either side, so there is a further mechanical reason for which end is on the busbar.

Some MCB rated for DC use do have a direction/polarity, but for AC I can't see any reason.

As far as up/down is concerned typically on a type A board the main switch or incomer RCD is fed from the top, but then the MCB/RCBO is fed from the bottom. However, for type B boards of course it is left/right!

I asked Hager once for the RCCB in a DIN board and was told either way is fine, as I checked the data sheet, etc, and at no point did it suggest a direction, but I wanted to be sure.

 

[LewisM]

Yeah this was for a custom panel where it wasn’t feasible to feed the bottom of the breaker so queried just to make sure it was complaint

 

[davesparks]

The MI tell you which end to connect to the busbar, and which end goes to the outgoing circuit.

Do they? The MI for a DB will tell you which way round they should be installed in that DB, but the MI for the actual circuit breaker is unlikely to say anything about it.

If you fit a circuit breaker incomer to the DB then you will have the live side at the bottom of the incoming circuit breaker and the live side at the top of the outgoing circuit breakers.

 

[Flanders]

I’ve been told the exact opposite from Hager technical support, direction doesn’t matter and doesn’t effect operation at all.

I will speak to hager again and get a second opinion

 

[pc1966]

This is what I got on 22/6/2020

Good Morning [pc1966],
Apologies for the delay, in regards to your question, the answer is no.
Our Main switches & RCD are neither pole dependant and makes no difference if you feed the supply from the top nor bottom.
I hope this answers your question.
Kindest regards,
Fraser
Technical Support

Hager Ltd
Hortonwood 50
TELFORD,Shropshire TF1 7FT
United Kingdom