Is a simple switch of b to c type mcbs going to appropriate here?

Robbiemikeyd · Feb 17, 2021

Hello and thanks in advance for any replies.

Moved into a new house with garage. My table saw... (https://www.axminstertools.com/axminster-trade-at254lts-table-saw-105573)...is causing the b16 mcb to trip in the small consumer unit in the garage. It is a relatively new saw and don't think it is a short causing the trip but the surge which apparently characteristic of table saws. Garage is powered via a bs5467 armored cable to the main consumer unit in the house, probably atleast 15-20m, with a b40 mcb.

Alot of forums say just to switch out the b's for c's but that sort of general advice sounds a bit too simple! Will that work? Will I need to switch out both mcbs to c type, or will the 40amp in the house cope with the surge ?

Thanks again
Rob

SJD · Feb 17, 2021

The maximum value and type of the MCBs (both the 40A distribution circuit to the garage, and the 16A final circuit in the garage) are determined by several factors - cable ratings, meeting disconnection times, voltage drop.

It might well be acceptable to change the B16 to a C16 in the garage, or it might well not be. Unless you are familiar with measurements like Ze, Zs, and know the cable sizes & electrical lengths, probably safer to say you need to get someone in who is (i.e. an electrician).

Wilko · Feb 17, 2021

Robbiemikeyd said:
Alot of forums say just to switch out the b's for c's but that sort of general advice sounds a bit too simple! Will that work? Will I need to switch out both mcbs to c type, or will the 40amp in the house cope with the surge ?

Hi - you are right, it is too simple to be true. The substitution can only be made if the loop impedance is sufficiently low, which can’t be ascertained without a test instrument. Unfortunately the link to the tool didn’t work

Robbiemikeyd · Feb 17, 2021

Axminster Trade AT254LTS Table Saw

This compact table saw has a laser cut, welded steel chassis, supporting the entire workings of the machine on widely spaced trunnions. A cast iron frame supports the motor and blade arbor, giving plenty of rigidity and blade support. The blade height...

www.axminstertools.com

Linked again just for people's reference.

Thanks for the replies. I was hoping a bit of calculation could be done off the back of the details given but I will probably just get someone in. Could do with some more sockets and lighting out there anyway so might aswell get the thing all set up properly. Just have the missus nagging to get other jobs done in the house and need my table saw!haha never a quick fix.

brianmoooore · Feb 17, 2021

I'd try substituting a B20 for the B16 first. There's a Chinese made metal cutting saw that a few of my customers have that suffers from the same problem, and a B20 usually fixes them.