I've just noticed that the power supply to our garage (running fridge- freezer, 2 lights, tumble-dryer & whatever power tool I need to use (e.g. strimmer)) connects back to our consumer unit at a MT106 MCB (6A) - and this is also the upstairs socket circuit. I am now very surprised that this hasn't tripped every time we use the tumble-dryer (2700W).
Is there a large tolerance on these things?
Thanks in advance for any input
Paul
Is it possible that you've followed the cable incorrectly and it's not that trip at all but the ring-main one next to it?
See the graphs on
Don't think so - flipped the trip switch & all upstairs sockets went off & the garage lights went out!
Has it ever tripped? Is the CU correctly labelled?
I am guessing it is a Hager CU as it uses MT106 labelled MCBs. Hager are as good as you get for quality IMHO.
OK! Someone cocked up - sockets are more usually on a much higher capacity circuit.
You haven't one of those dubious copy mcbs from the far east which dont have any guts inside do you? I'd be very dubious if a 6A never tripped with a 3kW tumble drier hanging onto it. Easiest option would be to swap the mcb for a good one from a reputable source.
Sounds like that needs a bit of investigation - not really an appropriate mix of things on one MCB.
Possibly more than many people expect - it takes quite a high current to get them to trip instantly (i.e. the sort of current you get nailing through a cable etc, rather than plugging in a few too many appliances. The time it takes to trip on more moderate overloads will vary depending on just how much... So even with a constant load of 2700W, it could actually take it 5 mins or so to trip (possibly more if your mains voltage is less than 240V).
Note also that things like TDs won't draw maximum current continuously they will turn the heater off each time the drum stops and rests. They also probably won't use full power unless on the highest temperature setting. So that can extend the trip time further - possibly even enough to scape through with no trip.
But for what size MCB? You have to assume that the 6A MCB is there for reason.
Oops!!
Thanks for your help everyone, but I've taken a closer look in daylight & realise I was looking at the wrong MCB after all - the one I should have checked is a
32A which makes a lot more sense. (Face glowing gently red!)Paul
Sounds like you need a pro to check things out. A 6 amp MCB is for lighting - not sockets - and if this is wrong what else is?
Using a too small MCB on a circuit isn't a safety issue - but if it had been wrongly wired so a 32 amp one is on a lighting circuit the results could be dire.
:-))
Not to worry, easily done.
The only thing I would want to check now is how the lights have been fed from this circuit (if indeed they have that is!). Depending on circumstances the larger MCB may not be providing fault protection[1] to the typical cable sizes used for lighting circuits. Chances are if its just the garage lights, then they will have been fed from a fused connection unit somewhere on the circuit and hence there is nothing to worry about.
[1]
You know how I hate to say "I told you so"?...
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