FCU on ring to spur

Benway · 22 Nov 2005

Hello

I have a FCU in a bedroom on a ring (Cables in and out) If I want to change this to a spur (I know you're thinking why does he want to do this). Is the normal way to connect the old cable in a junction box (stick this in the cavity and just run the new cable to the spur?

Cheers

Normally I'd just do as above but I thought i'd double check as there are now rules for every thing, just off to inform the NHS that the clearout I performed this morning wasn't up to regs............

Adam_151 · 22 Nov 2005

can do this, make sure the cable from the jb to the fcu is 2.5mm² and the jb is accessable for inspection (the cavity part of your plan sounds very suspect...)

and yes, please tell us why

Benway · 22 Nov 2005

Flat is brick outer construction and timber inner, so the cavity is just the bit between this. Is inspection needed for regs or just good housekeeping? If so would a back box with a frontplate and terminal blocks inside be better than a junction box?

The reason why is a long a beautiful story that one day I will tell my grandchildren, also I'm scared to tell you lot.

Adam_151 · 22 Nov 2005

Benway said:
Flat is brick outer construction and timber inner, so the cavity is just the bit between this. Is inspection needed for regs or just good housekeeping? If so would a back box with a frontplate and terminal blocks inside be better than a junction box?

Screw connections are considered non mechanically sound, and must be accesable for inspection, there has been much debate about this and other issues, but suffice to say, a jb hidden would be against regs IIRC, and seen as bad practice. Also wiring in cavities is bad practice* (and jbs would be doubly so I should imagine)

Box with blank plate and terminal blocks sounds ok to me

* - (Cos if thermal insulation is later installed in the cavity, it could cause the cable to overheat, and also some insulation will have a chemical effect on the pvc cable and break it down, the cable might also if touching both sides of the cavity, provide a path for moisure to travel between them...)

dwain dibley · 22 Nov 2005

oh go on
we wont tell

Benway · 22 Nov 2005

Cheers, I'll go for the backbox/plate option. Heh, I just needed a supply that can be remotely swtched for a sort of home automation thingy, i hope that was unclear enough.

Benway · 22 Nov 2005

On this same subject, what are the rules/regs for using relays/contactors in household wiring?

cheers

Had a search but seems to mostly find pages where people cant spell contractor.

Benway · 22 Nov 2005

As in

[/img]

Steve · 22 Nov 2005

AFAIK, most mains voltage contactors are made to fit in DIN rail enclosures, not back boxes. And they are made so the "control signal" is isolated from the controlled circuit, so it needs a "control in" and "control out"

what are you trying to achieve? why have the contactor before the FCU? (being before the FCU it needs to be a 32-40A contactor, if it were after the FCU you would only need a 20A one. I expect there is a cost difference here)

ban-all-sheds · 23 Nov 2005

Benway said:
Hello

I have a FCU in a bedroom on a ring (Cables in and out) If I want to change this to a spur

Err - that FCU creates a spur for you....

(I know you're thinking why does he want to do this).

I cannot see why you would want to

Is the normal way to connect the old cable in a junction box (stick this in the cavity and just run the new cable to the spur?

That new cable is the spur.

What do you think this change will do for you that running the spur cable from the output of the FCU wont?

Why do you want to change a perfectly satisfactory arrangement to one which is less satisfactory (extra joints and less-than-ideal protection for the spur cable, even if it is allowed in the regulations)?

Benway said:
As in

http://img466.imageshack.us/img466/8421/wiringplan072ha.jpg[/QUOTE]

That's almost completely AAF.

It's also more work, and not as safe, as leaving the FCU where it is, and as crafty points out, means a higher rated contactor.

It also achieves nothing that leaving the FCU where it is doesn't.

Benway · 24 Nov 2005

All good stuff. Agreed about the DIN rail mounting for the contactors. Would it be wrong/against regs to have a securely mounted contactor in a box? Also does the control 'have' to be isolated or could I just run control out to N in the FCU?

First plan was a little 'involved'. MkII below

Adam_151 · 24 Nov 2005

That looks better, where is this control signal from?

ban-all-sheds · 24 Nov 2005

Benway said:
All good stuff. Agreed about the DIN rail mounting for the contactors. Would it be wrong/against regs to have a securely mounted contactor in a box?

No - but the important bit is "securely mounted" - you'll need a DIN-rail mount for the contactor to go onto, but you can get things like these:

rather than a short bit of actual metal rail.

Also does the control 'have' to be isolated

You should have a way to ensure that the control circuit doesn't become live if you need to work on it. Without knowing about it, can't say if you need an isolation switch.

or could I just run control out to N in the FCU?

What does that mean?

First plan was a little 'involved'. MkII below

http://img295.imageshack.us/img295/6337/wiringplan114vw.jpg[/QUOTE]
Looks fine.

Benway · 24 Nov 2005

Control will be from a PC through a thermostat.

Rail mount is just what I'm after, RS I take it?

Do the 'live' (Control +) and 'neutral' (Control -) for the control both have to come from the controller as in the diagram, or can I just use the 'live' from the controller and connect the 'neutral' to the FCU?

ban-all-sheds · 24 Nov 2005

Where does the power for the control circuit originate?

diynot

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FCU on ring to spur

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