Electrical Question

Is a radial circuit on 32a breaker a fire risk?

An electrician doing a PIR on my flat tells me the above is a fire risk. i would just like to confirm this, as he tested the installation and says it was very good. This seems a bit of a contradiction. Separately, he also considers my fuseboard requires an RCD as soon as possible. He may be right, but I would welcome a second opinion as my installation dates from well before I Jan 2005 and so is not subject to BS 7671: 2008.

11 Answers

Best Answer

The electrician is right on both counts the 32 amp radial if 2.5mm cable has been used is a fire risk added to the overload protection not being correct you also have no RCD protection against earth faults I would not sleep easy in your flat until both items had been corrected make sure your smoke detectors are working ok
hope this helps
if so hit the like button

Answered 16th Oct 2011


Member since 9 Oct 2008

Dear rjhmyers,

To answer your first point, it depends on the size of the cable on the radial circuit in question. The usual 2.5mm cable should be protected by a breaker no larger than 20amps (if a radial circuit as opposed to a ring). If it is a 4mm cable or larger, then a 32amp breaker is sufficient.

Regarding the RCD, no-one will come banging on your door to order an upgrade to a modern fuse board. However, the latest regulations are in place to maximise electrical safety in the home. By adding RCD cover, you will be adding an extra level of protection to your installation and to you, the residents of the property. Also, should you ever want any alterations or additions to your circuits, an electrician will be obliged to check if the circuit being altered has RCD cover. In most cases, this will be required, and if not in place he won't be able to go ahead with the work.

I hope this helps.

GZB Electrical Services Ltd

Answered 16th Oct 2011

Capital Rewire Limited

Member since 20 Feb 2011

Hi there
A radial circuit run with a 2.5 cable should not be supplied off a mcb greater than 20amp even thought 2.5 cable can withstand 26amps or so
If the load is greater than this and the mcb is rated at 32 amp the cable can over heat and the breaker still may not trip in time

so yes it's a fire risk and the installation is unsafe
But a judgment can be made of how big your property is or how many points on the circuit or is it really likely the circuit will be over loaded

If it was a restaurant I would have given a code 1
If it's a 1 bed flat with 4 points I would have given it code 2

Kind regards
A1 electrical

Answered 15th Oct 2011

A1 Electrical Contracts Ltd

Member since 28 Feb 2010

Yes it is, it should be on a Maximum 20amp

Answered 15th Oct 2011


Member since 6 Nov 2009

If the radial circuit is wired in 2.5 mm.sq.
it is a fire risk,32 A breaker is too big and have to be
Replaced with 16 or 20 A circuit breaker.
If the circuit is wired in 4 mm.sq,it perfectly ok.
Regarding the RCD protection,if you are not altering the installation,
could stay as it is,as it was up to the standards when it was done.
It is recommendation only to have an RCD fitted,this could save your life.
Most of the times it is possible to replace the main switch in the consumer
unit with an RCD instead of replacing the unit.
Hope this helps.

Answered 16th Oct 2011

Elman Ltd

Member since 6 Nov 2010


A standard domestic radial light circuit would be on a 6A or 10A MCB and run with 1.5mm twin and earth cable. It would only be on a 32A MCB if the cable was a bigger cross section and it was supporting a larger load like a shower or cooker.

According to current building regs all your sockets, outside circuits, bathroom and kitchen circuits should be protected by an RCD.

It sounds like good advice to me.

Best Regards


Answered 15th Oct 2011

Wandle Electrics and Fx-it Professional Handymen

Member since 28 Sep 2011

It all depends on the cable size,
If the circuit is wired on a 4mm then yes a 32a mcb is fine, but if it's only wired on a 2.5 then it should be a 16a mcb.
And yes a 30ma rcd must be installed ASAP. Current regs stipulate that everything should be covered by an rcd in cavity walls chased in less than 50mm.

Hope this helps

SJN Electrical Ltd

Answered 16th Oct 2011

SJN Electrical Ltd

Member since 26 Jul 2011

2.5mm2 20amp max
4mm2 32amp max
NICEIC Approved Contractor

Answered 23rd Feb 2017

NJC Electrical Services

Member since 1 Feb 2016

it would be best to update your fuse-board to the current regs, but a radial circuit should be on a 16amp breaker if wired in 2.5mm and 20 amp if wired in 4mm

Answered 15th Oct 2011

I Parker electricals

Member since 3 Mar 2010

not necessarily although it depends on what size cable has been used on the radial, 2.5mm will take upto 22amps whereas 6mm will take upto 40ish amps. if its 2.5mm then the cable would be overloaded and would melt before the breaker trips the circuit! that in my opinion is a fail on a pir.
as for the rcd its not a fail on a pir but should be a code 4, which is doesnt comply with current regulations. i would advise having one installed as it is a safety device.
thanks matt

Answered 16th Oct 2011

amd electrical

Member since 4 Aug 2008

Depends on what size cable you have in if its in 4mm then yes but if its 2.5mm then it needs to be changed to a 16amp breaker. And current building reg rcd protection should be installed if cables are chased in walls less than 50mm

Answered 19th Jan 2017

Berry's Electrics

Member since 16 Jan 2017

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