Can I Replace 16A MCB With a 32A? Ask questions and find answers to many subjects relating to electrics and electrical work

[tim091]

Two parts to this question:

1) Curious, why do the 4 breakers in my CU labelled as "down sockets" have different current ratings? Two are 32, one is 40 and one is 16.

If they are four ring circuits then why would they be different?

2) What has kicked this off is that I have just got a 2000W table saw in the garage and it trips the 16A breaker every time I try to use it. Research suggests this is very common and is due to the start up load of the saw spinning up being high.

Suggested solution is to change the breaker for a C type rather than a B. But would it also make sense when doing that to change it for a 32A one, or is there a reason a 16A has been specified for that ring?

[Mr White]

Protective devices are to protect the cable, not the appliance, so changing to a higher rated MCB means if there is a fault the cable can overheat and cause a fire before the protective device operates.

Why they are labelled as such is any ones guess.

I would be inclined to switch them off one at a time to see what they really do.

[collectors]

Chances are the 40amp is a cooker or electric shower, 32amp are rings & the 16amp is a radial for ???. You would be far safer upping the fuse to only a 20 amp C/type assuming the cable thats in the MCB is a 2.5mm or larger, & seeing if this is enough as 2.5 has a 24amp rating.
If the saw is a 110volt it will be quite likely the transformer that is tripping it, as this can add to the problem.

[tim091]

Thanks both. From trial and error I see that the16a circuit only supplies 2 dbl sockets in the garage, the boiler and the boiler controls, plus the garage light and outdoor light.

The CU (and the boiler) is in the garage as the garage is part of the house, so it looks like when the boiler was installed this radial (it is a radial) was added with the garage sockets (they are surface mount with the cable (2.5mm T&E) running on the walls).

The manufacturer of the saw has not been forthcoming in telling me what the startup current is (they don't seem to understand my question!) so I have just got a 16a C type and will stick this in (confident that the wiring will take the load) and if that doesn't work I will try a 20a C.

[collectors]

If the fuse upgrade fails to do the trick?, it could be quite likely the capacitor in the saw is breaking down. These are quite often in the handle of a saw or in the start switch & can very in size, but quite often look like the link below & cost between 5-10 pounds. What they help to do is give the motor an initial kick of electric to help get the motor get going & reduce part of the start up load. You must replace like for like & if you do this, make sure you are unplugged from the mains & on the capacitor short each of the two terminals to earth, one by one with some insulated cable as these can hold a charge & give a kick but once shorted to earth & discharged they are fine.
I have had to change 1 on a lathe & one on a band saw & it solved the problem of fuse tripping on one & slow starting on the other.
This is all assuming its not just an underrated fuse.


https://www.google.co.uk/search?q=saw+c ... WUHfj-mBHM:

[tim091]

Thanks @collectors, useful info. The saw is brand new so I would hope not a capacitor failing yet.

However, I swapped over to the C breaker yesterday and problem solved.

Thanks for all the input guys.