MCB change on garage circuit

NickB_99 · 7 Dec 2014

I had a new CU put in by an electrician about 12 months ago.
All fine with it, but I've found using my chop saw in the garage causes the garage circuit MCB to trip. All other appliances in there are fine.

If I run an extension from the ring main to either the ring covering the remainder of the house, or the kitchen ring (they are separate) then it works fine.
I've had a closer look at the CU and the garage (& conservatory) circuit is protected by only a 16A device, rather than 32A on the other two circuits.

Untitled

NickB_99
7 Dec 2014
1

The garage/conservatory circuit looks to 2.5mm T&E also.

It seems quite a hefty motor in the saw, so was thinking just to switch the MCB on the garage/conservatory for a 32A device.
The MK CU came from screwfix, so was wondering if the following would be appropriate?
http://www.screwfix.com/p/mk-sentry-32a-type-c-mcb/40707
Type C looks the same as the existing ones with MK brand just under the switch.

The MK kit (10 way, dual RCD) seems to come with 1x40A, 4x32A, 5x6A, so a bit surprised I've got 3x32A and 2x16A - unless maybe the spec changed from a year ago maybe?

EFLImpudence · 7 Dec 2014

It depends on several thing:

cable size, length and routing
affecting volt drop and fault current.

You cannot just change the mcb without knowing.

Do you have a certificate for the CU replacement? It mat show the relevant values.

ban-all-sheds · 7 Dec 2014

DIYnewbee99 said:
2.5mm T&E ... 32A device.

//www.diynot.com/wiki/Electrics:MCBtoCable

http://www.batt.co.uk/products/view/624/Table-4D5A

AndyPRK · 7 Dec 2014

You might get away with fitting a 20A one which maybe suitable for both the cable and the saw

333rocky333 · 7 Dec 2014

Even just a type "C" version of the 16amp may be enough to absorb the start surge.
Subject to testing of circuit for EFLI

NickB_99 · 7 Dec 2014

EFLImpudence said:
Do you have a certificate for the CU replacement? It mat show the relevant values.

Yes. Uploaded a copy. Garage is circuit 4.

Untitled

NickB_99
7 Dec 2014
1

RF Lighting · 7 Dec 2014

One of the most incorrectly filled out certificates I've seen in a long time. I wouldn't trust a single word of it.

flameport · 7 Dec 2014

DIYnewbee99 said:
Yes. Uploaded a copy. Garage is circuit 4.

Not good. Actually dreadful. Useless.

An easier to read version:

Untitled

flameport
7 Dec 2014
1

NickB_99 · 7 Dec 2014

flameport said:
DIYnewbee99 said:

Yes. Uploaded a copy. Garage is circuit 4.

Click to expand...

Not good. Actually dreadful. Useless.

Oh joy.

RF Lighting · 7 Dec 2014

Should look more like this. Note how all the boxes are filled in.

Untitled

RF Lighting
7 Dec 2014
1

Spark123 · 7 Dec 2014

Gotta love the serial numbers of the test equipment used

RF Lighting · 7 Dec 2014

Never seen a type A 60898 device either

and they're all 6kA devices in the photo of the cu. Also never seen 6.0mm² cable with a 4.0mm² CPC.

EFLImpudence · 7 Dec 2014

The only good thing is it says the CU is in the garage.

If true

, it should be very simple to do what you want.

NickB_99 · 7 Dec 2014

EFLImpudence said:
The only good thing is it says the CU is in the garage.

If true , it should be very simple to do what you want.

Please can you elaborate?

flameport · 7 Dec 2014

Untitled

flameport
7 Dec 2014
1

1. This is the size of the CPC (earth) within the cable. 6mm cable usually has a 2.5mm cpc.
2. This column is the type of device, for MCBs generally B or C. Possibly D. Maybe even K or Z in some unlikely installations. Certainly never A.
3 The breaking capacity. Usually 6 for domestic boards, 10 for others. Highly likely these are 6.
4. The RCD trip current, 30mA in this case. Other values are available. NA is not one of them.
5. Maximum loop impedance values. Generally copied from a table supplied with the certificate book. The newer versions of this certificate do not have this column.
6. These columns are for ring circuits only. The socket circuits 2 and 3 are probably rings. The others are not. In any case, the values would be totally different for each circuit - unless all of the circuits use the same cable sizes and are the exact same length.
7. Continuity in ohms, one of the two columns must be completed for all circuits.
8. Insulation resistance. Typical values for new or decent circuits would be in the many 100s. Old, damp, dirty etc. ones perhaps in the 10-100 range. 1.1 and below indicates they are totally wrecked and unsuitable for use. These figures are wrong.
9. Measured loop impedance. Why the alarm gets a value and the others do not is a mystery. If the 1.2 and 1.3 figures in the other columns are to be believed, this value can't be 0.86 anyway.
10. Trip times for the RCDs, which were apparently not tested at all.
11. Serial numbers of the test equipment used. Obviously used for some other purpose here.

diynot

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.

Are you a trade or supplier? You can create your listing free at DIYnot Local

MCB change on garage circuit

Similar threads