Which circuit breaker B or C rated

[Bluekingfisher]

Morning all,

Having treated myself to a new Jet PT310 from Axminster Tools, it arrived on Tuesday. I spent yesterday afternoon removing it from the crate and cleaning the oil from the cast surfaces.

It has a 16A commando socket and so I thought, no problems, I have my band-saw and spindle moulder (both 3HP) on a dedicated 16A ring. However when I plugged the thicknesser in and switched it on it tripped my 16A breaker on my consumer unit. I thought this odd, particularly as my SM and BS have no issues working on the breaker.

I am hoping someone with a little more electrical knowledge than me can advise.

The circuit breaker is labelled ‘B16’, a friend of mine suggested that I may need a ‘motor rated’ breaker?? I have never heard of this but my limited investigations have identified ‘C’ rated breakers also. Would a ‘C’ rated breaker be what my friend suggested and is this what I need. While I am about it, would I also need to upgrade to the C-20A breaker as well or is this overdoing things?

Any thoughts would be very much appreciated.

BTW – this seems a great machine, has anybody got one and what are you impressions of it.
The only thing I am not sure about is, the electrical cord with the 16A commando plug plug has a 2 pin plug on the other end of the cord which fits into a corresponding socket on the machine end i.e not hard wired into the machine. I’m not sure I like this aspect as it may be prone to disconnecting when in operation or from a slight knock.

Thanks in advance all.

David

 

[mbartlett99]

Hi

This isn't uncommon - sometimes you get away with it and sometimes you don't. The trouble is the inrush current being very high before it quickly settles down to its running current. The c rated breaker allows for this brief spike on startup. If it was tripping after startup then an upgrade to a 20A circuit (not just the breaker but the cabling as well) would be necessary. 3hp is operating on the edge of a 16A supplys capability as you've found out.

There's a couple of guys on here who really know the technical details of the differences in MCBs so you might want to wait for their input before shelling out your hard earned.

It seems that a lot of machines come with that sort of cord; my table saw has a Schuko (German) socket and a British plug which I assume is to cut costs for manufacturers - producing one machine for the EU and just varying the cord supplied.

 

[Bluekingfisher]

Hi

This isn't uncommon - sometimes you get away with it and sometimes you don't. The trouble is the inrush current being very high before it quickly settles down to its running current. The c rated breaker allows for this brief spike on startup. If it was tripping after startup then an upgrade to a 20A circuit (not just the breaker but the cabling as well) would be necessary. 3hp is operating on the edge of a 16A supplys capability as you've found out.

There's a couple of guys on here who really know the technical details of the differences in MCBs so you might want to wait for their input before shelling out your hard earned.

It seems that a lot of machines come with that sort of cord; my table saw has a Schuko (German) socket and a British plug which I assume is to cut costs for manufacturers - producing one machine for the EU and just varying the cord supplied.

Thanks for the input - What cabling do you recommend, I have 4.0mm twin and earth, so I think this part is OK. Not really a huge job to change the breaker but was hoping to establish if a C rated breaker covers the surge aspect and would a 16A surge breaker be OK or would it be safer or more practical to upgrade to the 20A as well. Hopefully someone will put me right. Thanks for the input.

David

 

[mbartlett99]

TBH I'd prefer not to reccomend, 9fingers etc are the guys who are actually qualified on this.

 

[siggy_7]

As has already been suggested, the problem is that induction motors draw very high transient currents on starting, and falls as the motor gains speed. A type B breaker will trip between with an instantaneous current about 3-5 times the stated value, for a type C this figure is 5-10 times. I would have thought you'd be fine with a 16A type C breaker, I wouldn't have thought you'd need to go higher spec than a type C and I would also think that going above a 16A rating is not good practice for otherwise unprotected machines drawing up to about 3kW under normal operation.

 

[Bluekingfisher]

As has already been suggested, the problem is that induction motors draw very high transient currents on starting, and falls as the motor gains speed. A type B breaker will trip between with an instantaneous current about 3-5 times the stated value, for a type C this figure is 5-10 times. I would have thought you'd be fine with a 16A type C breaker, I wouldn't have thought you'd need to go higher spec than a type C and I would also think that going above a 16A rating is not good practice for otherwise unprotected machines drawing up to about 3kW under normal operation.

Thanks siggy - I have just been down to my local electrical wholealers, they have pretty much told me what you have stated. Unfortunately they did not have any of the type C MCB's in stock, so another visit will be required.

 

[Blister]

I had the same problem with some of my equipment and fitted " C " type

some info here

http://www.tlc-direct.co.uk/Main_Index/ ... index.html

 

[Bluekingfisher]

I had the same problem with some of my equipment and fitted " C " type

some info here

http://www.tlc-direct.co.uk/Main_Index/ ... index.html

It was TLC I went to, unfortunately they had none in stock so I'll have to try them next week or CEF for equivalent MCB's