Replacing Mcb in cu

[Whittler1507]

Hi Newbie here hope this question is not too stupid,

I had a new CU fitted in to my garage workshop to put a 16 amp supply to my bandsaw.

This consisted of new cu with a single spur to the 16amp socket.

Said bandsaw has died and is to be replaced with another that needs to be on a 20 amp circuit. This is because of the current/amperage draw needed during start up and braking.

Which I think means replacing the Mcb with one rated for 20 amps.

The sockets are the blue bayonet type connectors which I think can take it, the cabling is 2.5mm which Runs from socket to cu a distance of approx 5m and think it can take it, am I correct in thinking that I can just get the Mcb replaced?

Also would this require another certificate/sign off?

Many thanks


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[tomspark93]

The socket should be marked somewhere with the max current rating. Some are rated at 16A and others at 32A. The 2.5mm cable would be fine on a 20A Type B Circuit Breaker as long as installation methods are such that it doesn't de-rate the cable to less than 20A and the Earth fault loop impedance of the circuit doesn't exceed 1.75 ohms.

 

[Chivers]

Does the manufacture of the bandsaw state what type of breaker is required in the instructions?

 

[telectrix]

probably a simple swap of the MCB to a 20A, but to be certain, get a local electrician to do the job as he/she will ensure that the circuit is safe and compliant. for the sake of an hour's work. The replacement MCB must be same manufacturer as the original in order to maintain the integrity of the CU.

 

[Whittler1507]

Yes it needs a 20 amp type C Mcb


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[telectrix]

the type C MCB means that the EFLI is more critical, typically 0.87 ohms as opposed to 1.8 ohms. needs test gear to determine so as my previous post. get an electrician in.

 

[Octopus]

the type C MCB means that the EFLI is more critical, typically 0.87 ohms as opposed to 1.8 ohms. needs test gear to determine so as my previous post. get an electrician in.

Which could mean, if the shed is a distance to the main board, and the cable is small, you may not achieve this value - which in turn WILL raise other questions and costs.

Best get the sparks to do a Zs at the shed board when they come to quote.

 

[davesparks]

The blue socket which you have will almost certainly be rated at 16A so you cannot just put a bigger mcb on it.

The next size of socket available is 32A


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[telectrix]

The blue socket which you have will almost certainly be rated at 16A so you cannot just put a bigger mcb on it.

The next size of socket available is 32A




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the 20A C type is recommended by manufacturers.this MCB is to protect the cable, nothing else, and Zs value should be within spec. if the manufacturer has deemed that a 16A plug/socket arrangement is adequate, then we only need to apply calcs/ for the circuit.

 

[davesparks]

the 20A C type is recommended by manufacturers.this MCB is to protect the cable, nothing else, and Zs value should be within spec. if the manufacturer has deemed that a 16A plug/socket arrangement is adequate, then we only need to apply calcs/ for the circuit.

Seriously?
A single 16A socket protected by a 20A mcb is not right in my opinion. By the very nature of being a socket outlet anything could be plugged in to it overloading it.

 

[Flanders]

Yes a agree with dave if the machine pulls more than 16 amps then the socket will require upgrading to 32 amps (which is the next size up available ) or hard wire the machine into a 20amp isolator

 

[Risteard]

Seriously?
A single 16A socket protected by a 20A mcb is not right in my opinion. By the very nature of being a socket outlet anything could be plugged in to it overloading it.

It shouldn't overload it as if the appliance had too heavy a load it shouldn't be fitted with a 16A plug in the first place.

I don't believe there is any problem with protecting a 16A commando socket with a 20A device, although the protective device should not exceed 20A. This way you could have more than one commando socket on the circuit if you wished.

 

[Risteard]

Also would this require another certificate

Yes. It would.

 

[davesparks]

It shouldn't overload it as if the appliance had too heavy a load it shouldn't be fitted with a 16A plug in the first place.

I don't believe there is any problem with protecting a 16A commando socket with a 20A device, although the protective device should not exceed 20A. This way you could have more than one commando socket on the circuit if you wished.

And if they plug an adaptors in to connect multiple appliances?

Maybe I have a different view on this because in theatre we use 16A commando as the standard connector so I am used to anything and everything being plugged in along with every adaptor under the sun.

 

[Risteard]

And if they plug an adaptors in to connect multiple appliances?

Maybe I have a different view on this because in theatre we use 16A commando as the standard connector so I am used to anything and everything being plugged in along with every adaptor under the sun.

I would generally prefer to see a 16A device on it but a 20A isn't actually prohibited. I think Guidance Note 1 may even mention the arrangement.

Usually it would only be done where the load profile is known.