Non-motoring > work room power tripping Miscellaneous
Thread Author: nyx2k Replies: 14
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New Sun 5 Feb 12 18:23 
 work room power tripping - nyx2k
i have a twin socket in my workroom and today bought a new 2.2kw mitre saw and its trip the breaker 3times. the breaker is a 16amp one under the stairs and its seperate for the workroom ie the room has a dedicated circuit.

do i raise the circuit breaker ampage but the tumble dryer id 13smps and is ok so is the inducion motor drawing too much power at start up?

the tuble dryer isnt used at the same time as the saw.
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New Sun 5 Feb 12 18:31 
 work room power tripping - Zero

>> do i raise the circuit breaker ampage but the tumble dryer id 13smps and is
>> ok so is the inducion motor drawing too much power at start up?

Is it tripping at start-up? I guess it is.

Up the circuit breaker.
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New Sun 5 Feb 12 19:24 
 work room power tripping - nyx2k
yes it cuts at start up, about one time every 4 starts.

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New Sun 5 Feb 12 19:59 
 work room power tripping - Slidingpillar
Electric motors generally take far more than running current at start up.

A fuse run on a slight overload will not blow if it does not get too hot, so a 13A fuse may pass 14A for quite a while. Generally though, a breaker is magnetic and will trip in a very short space of time, even if the load is only slightly in excess.

Bit of a simplification but hopefully you get the idea.
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New Sun 5 Feb 12 20:06 
 work room power tripping - sherlock47
I think that probably the best solution is to turn the radial circuit with the 16A MCB into a 'ring' with a 30A mcb, by adding an extra 2.5mm cable from the consumer unit to the socket in the workroom. (This requires however that the existing cable run is in 2.5mm cable).

As an alternative, run an extension cable from a ring socket somewhere in the house for the use of the saw in the work room. It all depends on the geography of your situation.
Last edited by: pmh on Sun 5 Feb 12 at 20:08
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New Sun 5 Feb 12 22:29 
 work room power tripping - henry k
>>As an alternative, run an extension cable from a ring socket somewhere in the house for the use of the saw in the work room.
>>
In addition check the rating of the fuse in the extension lead and ensure the cable is all unwound.
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New Sun 5 Feb 12 20:12 
 work room power tripping - Kevin
A word of caution. Check the wiring before deciding to change the circuit breaker.

If it's a spur with 2.5mm cable you'll be limited to a 16A or 20A breaker depending on the length of the cable. If it's a ring with 2.5mm cable you should be able to use a 32A breaker.

A 2.2KW induction motor will be pulling around 10A under load but the startup current will typically be at least twice that and could be much more.
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New Sun 5 Feb 12 22:06 
 work room power tripping - Fursty Ferret
Startup current for a 2.2kW induction motor can be as high as 50A. Can't you just put it on its own C-curve 16A breaker?
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New Sun 5 Feb 12 22:19 
 work room power tripping - nyx2k
way to technical now for me :-)

the cb is 16amps now and is on its own circuit.
would i be safe putting a 30amp cb in the consumer unit?
if not i could use another circuit with extenion from the kitchen
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New Sun 5 Feb 12 22:23 
 work room power tripping - sherlock47
would i be safe putting a 30amp cb in the consumer unit?

NO based on what you said so far. If it is a radial circuit using 15mm or 2.5mm cable.
Last edited by: pmh on Sun 5 Feb 12 at 22:25
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New Mon 6 Feb 12 03:01 
 work room power tripping - Iffy
I've no technical expertise, but the advice given so far looks sound to me.

Is this the type of job which the householder is not supposed to tackle under those regulations which ban non-qualified people doing much more than changing a lightbulb?

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New Mon 6 Feb 12 10:12 
 work room power tripping - Fursty Ferret
As you've guessed, the problem of induction motors tripping circuit breakers is not uncommon.

A circuit breaker won't trip instantly when an over-current condition is detected. Domestic circuit breakers follow a B-curve (the curve determines how long the breaker will remain closed for a specific current), which will typically open the breaker very quickly in the event of an instantaneous overload.

This causes problems for you as you'd like to exceed the rated capacity for a short period, which brings us onto C-curve circuit breakers. These still trip if 16A (or whatever) is exceeded for any continuous length of time, but will tolerate about a 5x overload for a few seconds.

Screwfix:
www.screwfix.com/p/wylex-16a-single-pole-type-c-mcb-6ka/94594
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New Mon 6 Feb 12 11:47 
 work room power tripping - nyx2k
that sounds like what ineed as its always on startup of the motor and never on the tumble dryer which drawa more current.

i'll go over to screwfix in the morning. looking at it it looks like 2 simple screws but is it ok for me to change or do i need an electrician
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New Mon 6 Feb 12 17:56 
 work room power tripping - Dave_
>> but is it ok for me to change or do i need an electrician ?

It's not an electrician-only job, if that's what you mean. Anyone with enough nous to use a 2.2kW mitre saw would be fine with swapping a circuit breaker in a consumer unit.

Just remember to turn the master switch off first ;)
Last edited by: Dave_TDCi on Mon 6 Feb 12 at 17:57
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New Mon 6 Feb 12 21:57 
 work room power tripping - nyx2k
i'll drive over to screwfix in the morning.
this works by not tripping out immediatly it senses 3-4kw on startup?

today i plug an extension into the cooker socket as this has its own circuit aswell i think with the on off switch for cooker side and another socket which i prsume is 32amps like the oven. it didnt trip all day.
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