4mm radials

[JonathanA]

Morning all,

I‘d really appreciate some advice - not a kick in the pants please - from those more knowledgeable than me!

My new kitchen and utility room are each supplied by 4mm T&E radials. Each circuit is protected by a 32A RCBO.

Kitchen

• Single oven rated at 2.5kW connected to single socket at end of radial
• Toaster, kettle, fridge and microwave connected to 3 x double sockets leaving some spare

Utility

• Washing machine connected to single socket
• Vented dryer connected to single socket
• Boiler connected to 3A fused switch
• 2 x double sockets spare

Length of radial in both cases is less than 10m so no worries there.

I was told that a 4mm radial with 32A protection is a ’standard circuit’ but there are issues with the installation that bother me, specifically:

1) The oven is not on a separate circuit so it’s not a ‘standard circuit‘ at least according to the OSG
2) The cabling for the most part is clipped direct but it is boxed in with other loose cables for a run of about 2m.
3) All the cables from the consumer unit descend loosely through a void in an otherwise insulated stud wall before going their separate ways (I suspect my OCD is kicking in with this one)

My worry of course is the possibility of the 4mm cables becoming overloaded at less than 32A.

Please understand that rewiring either of these circuits or installing new ones would involve huge disturbance which I am very keen to avoid.

I would sleep easier if the RCBOs were down rated to 25A but Wylex only make compact types for this rating which wouldn’t match the others in the CU.

I’d really appreciate your advice on this. Best response would be to tell me it’s fine, that I’m overthinking it and should get a life!

Thanks, J

 

[buzzlightyear]

Please understand that rewiring either of these circuits or installing new ones would involve huge disturbance which I am very keen to avoid.

I would sleep easier if the RCBOs were down rated to 25A but Wylex only make compact types for this rating which wouldn’t match the others in the CU.

why would you want to down grade to 25 amp has a 32 on 4mm is good ,and what sort of cu in now.

 

[pc1966]

Neither circuit is going to be at the full 32A unless you plug in some heaters to the spare sockets as well, and even then the proportion of time spend at full load is going to be short (e.g. 5 mins to boil a kettle of water, etc).

So while part of the run may be a little less than 32A rated, I doubt it is going to see that current at all, let along for long enough periods to cause damage. Usually it is poor connections that cause serious overheating!

The main limitation is you don't have much margin for anything larger in the way of oven/cooker, so anything fancy would probably need a new circuit put in for such a change. But for what you have, it seems fine.

 

[westward10]

Whether the circuit may or not achieve 32A in normal use not forgetting this cannot be predicted with socket outlets, if the installation method does not permit a 32A protective device then they should not be used.

 

[Mike Johnson]

To paraphrase your question "your overthinking it and should get a life!" ? the only foreseeable problem could be in the future as pc1966 mentioned if you change your cooker or hob, especially if the hob is an induction type that can't be run off a 13amp plug, these have limitations on how many zones can be on at the same time.

 

[loz2754]

Method 103, in insulation in a stud wall-
4mm² 17.5 amps.

 

[westward10]

To paraphrase your question "your overthinking it and should get a life!" ? the only foreseeable problem could be in the future as pc1966 mentioned if you change your cooker or hob, especially if the hob is an induction type that can't be run off a 13amp plug, these have limitations on how many zones can be on at the same time.

That is not the only foreseeable problem you have socket outlets with an unpredictable loading.

 

[Mike Johnson]

Perhaps my post should have said "one of the foreseeable problems" rather than "the only foreseeable problem"

 

[telectrix]

think P said cables in stud were loose.i.e. insulation moved away from cables.

 

[telectrix]

it'll never even get warm. unless a certain weed is being grown .

 

[loz2754]

I have to agree with @westward10 on this one.

The use of conventional final circuits implies that we accept all of the conditions for conventional final circuits. This includes the fact that diversity cannot be applied in this case, because diversity has already been factored in.
So the design current for each of the 2 radials has to be taken as 32 amps.

I understand and perhaps even agree with @pc1966 and others, that in practical terms it seems likely that there will not be a problem with overloading of the cables. But this doesn't change the fact that the circuits have not been properly designed to take into account the installation conditions.

I would be getting the electrician who installed it to correct his mistake at his own expense.

 

[Mike Johnson]

What mistakes has the original electrician made?

 

[loz2754]

think P said cables in stud were loose.i.e. insulation moved away from cables.

The 2 options for cables in a stud wall are:
103 in insulation with the cable not touching the wall.
102 in insulation with the cable touching the wall.

So if the cable was clipped in such a way that it is in contact along its length with the wall, the current carrying capacity would be 27 amps for a 4mm² cable.

 

[loz2754]

What mistakes has the original electrician made?

He has not allowed for derating the circuit because of thermal insulation.

 

[telectrix]

nowhere does OP say that the cable is in contact with insulation . i quote.

All the cables from the consumer unit descend loosely through a void in an otherwise insulated stud wall.

 

[pc1966]

I wonder if the OP can post some photos of the cable run to take a look? Also a detailed photo of the Wylex board to see what it is using?

Certainly changing to a 25A RCBO would deal with most installation methods for 4mm, the question is if one can be sourced for the board. I'm willing to bet that @westward10 will know chapter & verse of what can be fitted!

 

[7029 dave]

This is the trouble with radial circuits for socket outlets, I like the flexibility of RFC any day, especially in kitchen.

 

[Deleted account]

4 mm radials are the future and are absolutely fine.

we are the only country in the world who do rings. What does that tell you.

in my opinion rings are potentially dangerous and I don’t do them any more. Radials every time for me.

personally I would have liked to put the oven on a separate circuit, but each electrician to there own.

ask 5 electricians what they think of an installation design you will get five different answers.

 

[pc1966]

we are the only country in the world who do rings. What does that tell you.

That we used fused plugs and no one else does?

 

[7029 dave]

4 mm radials are the future and are absolutely fine.

we are the only country in the world who do rings. What does that tell you.

in my opinion rings are potentially dangerous and I don’t do them any more. Radials every time for me.

personally I would have liked to put the oven on a separate circuit, but each electrician to there own.

ask 5 electricians what they think of an installation design you will get five different answers.

I agree with you statement about each to their own, talking about other countries, the radials are multiple just like we had before RFC, talking in general for instance 20A radial unlimited socket outlets is IMO ridiculous. I would never create such a circuit.
I remember at college in one of the craft principles book on craft theory (J F Whitefield) socket radials were limited cant remember the amounts between 15A and 30A circuits.