Extend Ring Main or add FCU?

Weeball · 19 Jan 2021

My wife and I have just bought a 1960s house. Currently there is only 1 Double Socket (DS) in our bedroom so I want to add three further DSs to the room – 1 new DS will be used for a hair dryer & hair straighteners, the existing and other 2 new DSs will be used for low demand items (i.e. LED bedside lights, alarm clocks, phone chargers, etc…). I need to check the existing DS is part of the ring main, but once I’ve confirmed it is, my plan was to extend the ring main from the existing socket (using a Wago box & 222 connectors and then joining back at the existing DC ). However, after doing some reading I’m concerned about the risks of extending the ring main as I don’t have the specialist kit needed to test things like volt drop and loop impedance. The only testing kit I have is a standard multimeter. To mitigate any risks, I’m now considering adding a spur from the existing DS to a 13amp FCU and then onto the 3 new DSs. My only concern here though is whether the current drawn by the hairdryer and straighteners would exceed the 13amp fuse in the FCU!

Would a 13amp FCU be sufficient to handle the current drawn by a hair dryer and straighteners if used at the same time?
What’s the better of the 2 options for me (i.e. split the ring main or add a FCU)?
Am I right to be concerned about extending the ring main or not?

In our previous home, I added single spurs to a lot of the existing DSs and completed various home lighting projects, so I’m fairly confident with these tasks.

Any advice would be greatly appreciated.

EFLImpudence · 19 Jan 2021

IF the socket is on the ring circuit, then use 4mm² T&E for the spur then you can have as many sockets as you want without the need for an FCU.

Read this:
https://www.diynot.com/diy/threads/...ion-to-add-a-these-additional-sockets.561394/

JohnW2 · 19 Jan 2021

Weeball said:
Would a 13amp FCU be sufficient to handle the current drawn by a hair dryer and straighteners if used at the same time?

That obviously depends upon the items in question - they should both bear some indication of how much power (watts) they each consume.

13A is roughly equivalent to 3,000 watts. My guess would be that the two items together might be close to, maybe over, that figure, but we won't know until you check.

Kind Regards, John

Weeball · 19 Jan 2021

Thank you so much for the response EFL and John. I really do genuinely appreciate it.

John - I’ve checked the hair dryer and straighteners and they’re 1800w and 50w respectively. Well under the 3000w you mentioned. I guess a 13a FCU would be more than adequate?

EFL - just to make doubly sure. After checking the existing DS is part of the ring main, I can run a spur off the back of the existing DS using 4mm T&E to the 3 new sockets and I don’t need a FCU?

Thanks again.

JohnW2 · 19 Jan 2021

Weeball said:
John - I’ve checked the hair dryer and straighteners and they’re 1800w and 50w respectively. Well under the 3000w you mentioned. I guess a 13a FCU would be more than adequate?

Indeed. I'm rather surprised that the straighteners use so little power!

Weeball said:
EFL - just to make doubly sure. After checking the existing DS is part of the ring main, I can run a spur off the back of the existing DS using 4mm T&E to the 3 new sockets and I don’t need a FCU?

I'm sure he'll answer himself, but .. Yes!

Some people might try to tell you that you shouldn't do that because it is not one of the examples given in the 'guidance' material in an Appendix of the regulations, but I would suggest that you ignore them, since there is nothing about it which contravenes the actual regulations

Kind Regards, John

EFLImpudence · 19 Jan 2021

Yes.

333rocky333 · 19 Jan 2021

Another option is to replace the Double socket with 2 singles, then you can extend the ring in 2.5mm by going from 1 single round the room and back to the other single,
Bare in mind new sockets now need Rcd protection, not always present in a 1960s house

Weeball · 19 Jan 2021

Cheers John.

I was surprised the straighteners were only 50w too!

John or EFL - am I able to follow the 4mm T&E spur approach for other rooms in the house too as long as I’m spurring from a socket on the ring main? And, when using 4mm T&E I’m not limited to the number of sockets I can add from 1 ring main socket?

JohnW2 · 19 Jan 2021

Weeball said:
Cheers John. I was surprised the straighteners were only 50w too!

It obviously can't take much heat to straighten hair!

Weeball said:
John or EFL - am I able to follow the 4mm T&E spur approach for other rooms in the house too as long as I’m spurring from a socket on the ring main? And, when using 4mm T&E I’m not limited to the number of sockets I can add from 1 ring main socket?

Yes and yes.

The one thing you should try to avoid is having many sockets too close to one end of the ring - but that applies to both sockets 'on the ring' and also to where (on the ring) you connect a 4mm² spur which is serving several sockets.

Kind Regards, John

winston1 · 19 Jan 2021

Much better to extend the ring though.

EFLImpudence · 19 Jan 2021

Why? Please tell us. I am genuinely interested if there is a reason.

Especially if both new cables (there and back) will be in the same place, you might as well connect them both to all the relevant sockets - or, here's a thought - use one larger cable.

JohnW2 · 19 Jan 2021

EFLImpudence said:
Why? Please tell us. I am genuinely interested if there is a reason.

I, too, would be genuinely interested to hear of any true 'reason' (why 'extending a ring' is better than spurring from it).

As recently (and often!) discussed, there is a potentially slight issue (although very slight when we have Method C 2.5mm² cable and a 32A OPD) in relation to where loads are, or may be, applied to a ring final - but that's as much of a potential issue when 'adding sockets to a ring' as when spurring from it.

Kind Regards, John

Weeball · 19 Jan 2021

JohnW2 said:
The one thing you should try to avoid is having many sockets too close to one end of the ring - but that applies to both sockets 'on the ring' and also to where (on the ring) you connect a 4mm² spur which is serving several sockets.

Thanks John. Out of interest, other than distance/location from the fuse board, is there any other way of determining where in the ring a socket is?

narkeybee · 19 Jan 2021

Trying to get two 2.5mm and a 4mm in the back of a DS might be difficult,easier to continue the ring.

EFLImpudence · 19 Jan 2021

narkeybee said:
Trying to get two 2.5mm and a 4mm in the back of a DS might be difficult,

I disagree.

easier to continue the ring.

But it isn't, is it?

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Extend Ring Main or add FCU?

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