Main CU change for assessment with garage small CU

[Midwest]

I'm doing a domestic CU change for my assessment. The client has an additional existing small CU, in his garage, wired from the ground floor ring main, suppling light and 2 x SSO. Firstly, is this a deviation from BS7671, i.e. no protective device on the supply cable other than 30amp fuse. If the client declines rectification, do I comment as such on the EIC. Secondly, do I complete another schedule of test results for this 'CU' (I think so, but just clarifying).

 

[crow11]

if your putting a new cu in the you will be getting rid of the 30A fuse, and replacing it with mcb with rcd protection in your new cu, what cu is in the garage at the mo, is it easy enough to run a new feed to it and have it on it's own mcb from new cu, yes you will have to do a separate schedule of test results for the garage as you are altering the characteristics of all the circuits by putting in a new cu

 

[Midwest]

I haven't sized the supply cable (to garage CU) yet, but I suspect 2c 2.5mm swa, which is rated at 28amp,ref meth.C (I'm doing pre work surveys/tests tomorrow).
The replacement PD for ring final is going to be a 32a RCBO, therefore the garage supply cable is not protected. CU in the garage has rewireable fuses. If I can't convince the client to run a new supply from the new CU, can I just make comment on the EIC? Happy now, with the additional schedules of tests.

 

[Ducksy]

The replacement PD for ring final is going to be a 32a RCBO, therefore the garage supply cable is not protected

If that garage supply is on that 32 rcbo then it will have additional protection

I don't believe there is anything against the regs the way the garage is feed from the ring at the moment

 

[GT1]

Is the supply cable to the garage appropriate ?
Is it overhead on a catenary wire, or underground and done in SWA..?
Is it terminated properly at both ends ?

If its not appropriate and customer won't rectify then disconnect from the ring, advise client and leave out of your scheme of work.
The client can pay to have you rectify it a later date.

 

[crow11]

I just presumed the garage was attached for some reason lol, all the 1's I seem to do are attached makes life a bit easier, how many way is the cu in garage and what size fuses are in now, and how is the cable run at the moment, and length of run only asking cause your on about connecting 28A cable onto 32A supply, I know you say it only as 2 sso in and a light but will he be adding more in the garage at any time, if so and he wants a new cable to garage would look at 4mm swa which would give you 38A ref method c, or put the new supply on 20A and then use 2c 2.5 swa you know what some people are like with welders and other tools

 

[Richard Burns]

I'm doing a domestic CU change for my assessment. The client has an additional existing small CU, in his garage, wired from the ground floor ring main, suppling light and 2 x SSO. Firstly, is this a deviation from BS7671, i.e. no protective device on the supply cable other than 30amp fuse. If the client declines rectification, do I comment as such on the EIC. Secondly, do I complete another schedule of test results for this 'CU' (I think so, but just clarifying).

If the circuit out to the garage is a spur off the ring then the cable would not be protected by a 32A MCB and spurs are only permitted to have one double socket unless fused down.
If the circuit to the garage is an extension to the ring then this would not be ideal but would comply with the regulations as the cable will be protected.
If you have the spur situation then you could ensure that the cable is protected by fitting a 25A breaker in your new CU for that ring circuit, whilst you would still have a spur having more than a double socket it would not be on a 32A ring, so would be in the realms of a safe circuit but not a standard circuit.

 

[Engineer54]

Just to be clear, ...is this supply out to the garage direct off the ring circuit or via a FCU??

 

[Midwest]

Thanks for your replies chaps. I've banked on using this CU change for my assessment. I'm retiring from my current job in two weeks and haven't anything else arrange to do for my assessment at the mo (at the end of April). The garage cu is fed by a swa cable, from the downstairs ring. As far as I can see there is no fcu, I say that because the sso I suspect where the connection is made is now behind a radiator! The client had a new rad installed, and the appropiate wall was where this socket is.
I guess if I wish to proceed with this is to convince the client to have an appropiate new supply, either via an fcu or completly new supply from the new CU with it's own circuit. Reason; because the garage cu supply cable does not have an appropiatly rated fuse to afford the cable with short/overload protection. Unless I derate the downstairs ring fuse rating, I must say I never heard of that before?

If the client declines, could I make comment on EIC?

 

[GT1]

You need to know what size the swa is before making a decision on its suitability for the task, then apply the various factors such as volt drop, installation methods etc etc.
my main concern would be how the swa has been terminated.. ie has it been properly glanded and the armour earthed.
If its a short run and assuming its a sensibly sized cable your almost certain to be fine with your figures to meet disconnection times at the ocpd.
And talking of which... Assuming that the client is not going to be arc welding or having sauna in the garage, then a 13A FCU off the ring should be ample for the odd power tool, strip light and a lawnmower.

 

[Midwest]

Yep noted, but as I've said there is no fcu I can see.

 

[Richard Burns]

When you are changing a CU the circuits that you connect to the new CU must be safe to use, you have to make a competent assessment of the circuits to determine this.

Lowering the OCPD for the downstairs ring may, if the customer has a lot of high power appliances on the downstairs ring (such as if it is also the kitchen socket supply), approach a problem with the MCB tripping out on overload, but this is not likely as one can also have 20A radial circuits, for instance. It would require an assessment of likely loading on the ring.

You are going to need to see the connection to the garage to ensure it is safely connected. Testing may help you determine how bad it is to start with.

This advice from the ESC Best Practice Guide 6 may help you assess what you can do
Consumer unit replacement BS7671 compliance:
5.1. Replacing a consumer unit in an existing installation is an addition or alteration to that installation. The work must therefore be designed, erected and verified in accordance with the requirements of the current edition of BS 7671, and must not impair the safety of the existing installation. (Regulations 110.1(xx) and 610.4 refer.)
5.2. BS 7671 does not require existing circuits to be upgraded to current standards in order for them to be connected to the outgoing ways of the replacement consumer unit.
5.3. However, circuits that are defective or noncompliant with the requirements of BS 7671 in a
way that would result in real and immediate danger must not be connected to the consumer unit.
5.4. Where a consumer unit is being replaced, additional protection by means of RCDs in accordance with
Regulation 415.1 should be provided to the extent required by the current edition BS 7671, such as for:
• socket-outlets (Regulation 411.3.3 refers),
• mobile equipment for use outdoors (Regulation 411.3.3 refers),
• cables concealed in walls or partitions, where required by Regulations 522.6.6 to 522.6.8, and
• circuits of locations containing a bath or shower (Regulation 701.411.3.3 refers).
5.5. Circuits that are to be provided with RCD protection must be divided between a sufficient number of RCDs or otherwise designed as necessary to avoid hazards and minimise inconvenience in the event of a fault (Regulations 314.1 and 314.2 refer).
5.6. The consumer unit must not be replaced until it has been established that:
• the rating and condition of any existing equipment, including that of the distributor, will be adequate for the altered circumstances, and
• the earthing and bonding arrangements necessary for the safety of the alteration or addition are also adequate. (Regulation 131.8 refers.)
5.7. Any defects found in the reconnected circuits must be recorded on the Electrical Installation Certificate covering the replacement of the consumer unit, as required by Regulation 633.2

 

[Midwest]

Client has adopted using RCBO's for all circuits, so that covers 5.4 & 5.5. The meter tails are being replaced with 25mm & 16mm ET & main bonding with 10mm, so that covers 5.6,and the new CU will not result in 5.1. So I'm just left with 5.2&3. The garage is only used as storage, outside tools - lawn mower etc & indoor appliances - fridge freezer etc. Therefore unlikely there will be an overload of the supply cable and short circuit will be covered by RCBO, so don't believe there is 'real and immediate danger', so don't think 5.3 applies. So could I just note on the EIC as in 5.7?

I'm not happy leaving the circuit as is and will try & convince client otherwise, but just checking the position when asked by my assessor?

 

[Engineer54]

If it is almost impossible to change the existing situation, then personally i would replace the main switch in the garage CU for a suitably sized DP MCB of say 20A or 16A, RCD protection being provided by the OCPD at the house CU!!. At least that way, you shouldn't be able to overload the spurred cable... Not ideal but a still a suitable solution!!

 

[Richard Burns]

Client has adopted using RCBO's for all circuits, so that covers 5.4 & 5.5. The meter tails are being replaced with 25mm & 16mm ET & main bonding with 10mm, so that covers 5.6,and the new CU will not result in 5.1. So I'm just left with 5.2&3. The garage is only used as storage, outside tools - lawn mower etc & indoor appliances - fridge freezer etc. Therefore unlikely there will be an overload of the supply cable and short circuit will be covered by RCBO, so don't believe there is 'real and immediate danger', so don't think 5.3 applies. So could I just note on the EIC as in 5.7?

I'm not happy leaving the circuit as is and will try & convince client otherwise, but just checking the position when asked by my assessor?

If you believe that there is no "real and immediate danger" then you have made an assessment of the circuit to this effect.
If you then inform your assessor of the fact that you have assessed the circuit and noted down the non compliance with the regulations then you may be OK as it will show that you are aware of the situation and have made attempts to rectify it and taken account of the hazards and risks associated with it.
However it is your decision at the end of the day what you do as you are the competent person on site.