Electric Panel Heater on radial circuit

[Johan2218]

Hi,

We have a garage not far from house that has been converted a few years ago in to a usable room.
We want to put in an electric panel heater (likely just that rather than an oil filled one) and wall mount it.

Found a 2kw one with built in timer and manufacturer supplies it with a moulded plug and says it's absolutely fine to plug in (or permanently fuse spur it).

There is a second consumer unit in the garage installed only a few years ago from the main house board (also new at the time) proper armoured cable etc. It's all been registered as an installation at the council, approved etc.

In the garage there are 3 sockets to one 20amp fuse on the board but I note they have done this as radial rather than a circuit returning to the board, normal 2.5mm T&E used. So it runs to the first socket, from there to second socket and then to third where it terminates. This heater will be on the first socket and nothing heavy will get used anywhere else, no power tools or other heaters etc.

My question please, any issue in plugging this 2kw unit in to a radial circuit rather than a more normal ring one?

Thanks.
John

 

[Murdochcat]

It all depends on what else is plugged in. 2Kw is about 8 Amps ..............

 

[martygturner]

You have a 20 amp breaker therefor it can power 20 amps, as the heater is 8 amps whats the issue and remeber thats its maximum load, it might draw 8 amps to start with then as it hits temp that will ramp down. As it has a plug why would it not be ok to plug into a standard socket.

 

[flameport]

My question please, any issue in plugging this 2kw unit in to a radial circuit rather than a more normal ring one?

No.

The vast majority of circuits are radials.
Rings are not 'normal', they are a special case designed for a set of particular circumstances that existed 70+ years ago.

 

[Johan2218]

Thank you to everyone...very helpful.

 

[FrodoOne]

The vast majority of circuits are radials.
Rings are not 'normal', they are a special case designed for a set of particular circumstances that existed 70+ years ago.

"The ring circuit and the associated BS 1363 plug and socket system were developed in Britain during 1942–1947.
They are commonly used in the United Kingdom and to a lesser extent in the Republic of Ireland.
They are also found in the United Arab Emirates, Singapore, Hong Kong, Beijing, Indonesia and many places where the UK had a strong influence, including for example Cyprus and Uganda."
(https://en.wikipedia.org/wiki/Ring_circuit )

In many countries they are "Not Allowed".

 

[ebee]

No.

The vast majority of circuits are radials.
Rings are not 'normal', they are a special case designed for a set of particular circumstances that existed 70+ years ago.

Ring Final Circuits are common in the UK(mainly) and were designed for certain circumstances that exist a while back.
I do realise that some dislike them nowadays but they are here today and have been for years. Seem unlikely to be disallowed anytime soon and even if outlawed today there are still billions in service now and for years to come so we need to be able to test/add/modify them for the next few thousand years or so.
For some strange reason there are some that not only do not dislike them but rather than just like them they consider them the only proper method of wiring sockets, I have no idea why they might think that.

I do note that Flameport and I seem to be on opposing sides on ring final circuits but I think we tend to agree on pretty much everything else though.

It does depend a bit on age of installation and the local area of the installation and the age and mindset of folk using/installing them.
To me, rings are quite normal.

Anyway, if something is manufactured with a plug and flex on it then it will usually be OK just to plug it in to a conventional circuit of any persuasion.

 

[Murdochcat]

Rings are practical in kitchens. Radials elsewhere

 

[martygturner]

For some strange reason there are some that not only do not dislike them but rather than just like them they consider them the only proper method of wiring sockets, I have no idea why they might think that.

I agree, from a letting owners point of view they are a pain in the butt. We have them removed at every EICR. From a landlords perspective when a ring trips that's it, emergency electrician if you can find one, from a tenants perspective lost days work waiting in. With a set of radials any faults the tenant still has other radials working and can keep modern life going.

 

[ebee]

Rings are practical in kitchens. Radials elsewhere

Can you elucidate on that statement please? thanks

 

[ericmark]

If we had sockets which could take three 6 mm² cables then we could fit 32 amp radial circuits with ease, however they in the main don't, getting three 2.5 mm² into some sockets is hard enough, so with a radial using 2.5 mm² we are limited to 20 amp, better than in many other European countries which if they follow rules, radials are limited to 16 amp, can't have a 16 amp unfused socket which can take an unfused plug rated at 16 amp with over a 16 amp supply overload.

I remember my grandfather's house, with a fuse box full of little re-wire-able fuses, every socket had it's own fuse. The 13 amp plug which except for medical life dependent equipment are always fused, allows for multi-sockets on both rings and radials with a few rules which need to be followed, and tradition is when we started having multi-ring circuits, the house was split side to side, so with a ring final failure there was no need to run extension leads up/down stairs and both ring finals had a similar load.

The RCD however changed that, since lights split up/down, and we wanted the lights to stay on if some one caused the RCD to the sockets in that room to split, and most consumer units only had provision for two RCD's the sockets needed to split same as lights, so no room had sockets and lights on the same RCD, now with RCBO's we can return to side to side split.

The chance of having two heavy power user on the same circuit at 20 amp is far higher than having three heavy power user on the same circuit at 32 amp, we use the formula when working out likely volt drop, 20 amp centre/end, and rest even spread, so with a 20 amp radial we use 20 amp as figure to work out volt drop, and with a 32 amp radial or ring, we use 26 amp to work out volt drop. So our maximum lengths are:-
Ring final with 2.5 mm² cable and 32 amp overload - 106 meters.
Radial with 2.5 mm² cable and 25 amp overload - 28 meters.
Radial with 2.5 mm² cable and 20 amp overload - 32 meters.
Radial with 2.5 mm² cable and 16 amp overload - 42 meters.
Radial with 4 mm² cable and 25 amp overload - 42 meters.
Radial with 4 mm² cable and 20 amp overload - 56 meters.
Radial with 4 mm² cable and 16 amp overload - 71 meters.
From the above it is clear why we still use ring finals, OK since there and back 106 meters is only a max of 53 meters from distribution unit, but when wiring easy, one 100 meter role of cable must not be exceeded with a ring final. A little more of a problem extending existing, either R1+R2 or the loop impedance / prospective short circuit current as centre of ring final or end of radial needs to be measured, and the volt drop calculated, the radial with 4 mm² cable and 25 amp overload with 0.35 Ω at incomer looking for less than 0.99 Ω at the end of the radial, the 25 amp overload with 2.5 mm² is a problem, as easy to exceed 28 meters.

However although we normally use 20 amp plus half of remaining that is not a regulation, one can use other figures, and often we find all the person doing an alteration looks at is the min current to trip the overload within the prescribed time, that is a regulation. And I have to admit going over the 5% volt drop allowed is unlikely to cause problems, there are a few items where volt drop is critical, fluorescent lights with wire wound ballasts, and non inverter drive refrigeration units, have found shrink wrap machines fail due to volt drop, but they are not really used in the home.

But the installation should be designed, that does not mean use a ring final as that is what we have always done.

 

[EFLImpudence]

Most are missing the point or don't know it.

It is not merely a matter of personal preference.

The UK ring circuit was designed at the time for use with 30A BS3036 fuses - with which a 30A radial would require 6mm² cable - and the regulation still only allows the conditions relating to these fuses; it has not been updated to take account of the conditions when using MCBs where a 40A MCB or 1.5mm² T&E could be used.

So, perhaps far from being a good idea, they are in fact unnecessarily restrictive and a waste of cable and/or capacity.

Perhaps the rest of the world think them unnecessary simply because that is the case.

 

[Harry Bloomfield]

I agree, from a letting owners point of view they are a pain in the butt. We have them removed at every EICR. From a landlords perspective when a ring trips that's it, emergency electrician if you can find one, from a tenants perspective lost days work waiting in. With a set of radials any faults the tenant still has other radials working and can keep modern life going.

That is just as dependent on the number of radial circuits, as it is on the number of ring circuits in the premises.

Here I have two rings, and around five radial socket circuits. Both methods have their good points.

 

[JohnW2]

.... the regulation still only allows the conditions relating to these fuses; it has not been updated to take account of the conditions when using MCBs where a 40A MCB or 1.5mm² T&E could be used.

It's not just a case of 'lack of updating'. There is no rational electrical reason why Method C 1.5mm² T+E could not be used for a ring final' given that even with 2.5mm² T+E, the CCC is allowed to be as low as 20A (for the installation method utilised).

However, I'm not so sure about a 40A MCB, so long as the reg continues to only require a minimum CCC of 20A. With that CCC, if the circuit were loaded to its full design current (40A) some of the cable would inevitably be 'overloaded' unless the load were perfectly 'balanced' on the ring.

 

[EFLImpudence]

... the regulation still only allows the conditions relating to these fuses; it has not been updated to take account of the conditions when using MCBs where a 40A MCB or 1.5mm² T&E could be used.

If a circuit is electrically compliant with a 30A BS3036 fuse then this could be replaced by a 40A MCB.