16 amp supply - Brightspark!

[rorie]

thats just a double pole mainswitch the 2 way means it will accept 2 minature circuit breakers.if u have a 6mm cable feeding your garrage fit a 32 amp mcb in that unit

So that unit will have a main 'on/off' and then i need to add in a MCB? In which case i may as well add a 'garage unit' which already comes with the MCB.

The CU in the garage has a 63amp RCD protection. I never expect to see that sort of usage as only using one power tool at once. But should the MCB in the house not equal that value?

 

[Sidewinder]

So, that does not cause losses.

OP what saw is it?
Exact make & model please and I may be able to throw some light on it.

We are an authorised warranty repairer for a lot of kit by some big names.

 

[brightspark]

what is the full load amps and size motor on your saw ??and how far is it from the main supply in house ??

 

[Sidewinder]

So that unit will have a main 'on/off' and then i need to add in a MCB? In which case i may as well add a 'garage unit' which already comes with the MCB.

The CU in the garage has a 63amp RCD protection. I never expect to see that sort of usage as only using one power tool at once. But should the MCB in the house not equal that value?

NO!
The circuit breaker is there to protect the supply cable and has nothing to do with what you expect to use, unless the whole system is coordinated correctly.
An RCD must be rated at or above the current protection for the circuit (load) to be correctly sized.

 

[rorie]

its the axminster AW10…. and brand new! I called them and they told me the 'not latching' must be due to a faulty NVR, but they cannot confirm unless i get rid of the other possible faults until i get it onto a 16 amp supply. The new NVR is sitting here ready to be installed, but keen to fix the supply too so that i know there are no other possible faults (other than the saw its self)

 

[brightspark]

So that unit will have a main 'on/off' and then i need to add in a MCB? In which case i may as well add a 'garage unit' which already comes with the MCB.

The CU in the garage has a 63amp RCD protection. I never expect to see that sort of usage as only using one power tool at once. But should the MCB in the house not equal that value?

the 63 amp is the current that the rcb can handle it will have a 30 milliamp trip for earth leakage u still need the minature circuit breakers fitted for overload

 

[Sidewinder]

its the axminster AW10…. and brand new! I called them and they told me the 'not latching' must be due to a faulty NVR, but they cannot confirm unless i get rid of the other possible faults until i get it onto a 16 amp supply. The new NVR is sitting here ready to be installed, but keen to fix the supply too so that i know there are no other possible faults (other than the saw its self)

OK, I used to do warranty repairs for Axminster.
So I know their kit quite well.
First, as BS asks we must know the motor rating plate details.
Then we need to know the cable sizes and lengths back to the DNO fuse, that way voltage drops can be assessed to be sure that the starting load of the motor is not "pulling" the supply voltage so low that it is below the value at which the "NVR" (I hate that term!) will not retain.

 

[rorie]

An RCD must be rated at or above the current protection for the circuit (load) to be correctly sized.

Well i wouldn't have expected that! So at the house i need a DP switch (as RCD is not needed) and a MCB at a value less than or equal to the 63amp RCD in the garage. A 32 amp should be fine as that is the max rated MCB in the garage.

how far is it from the main supply in house ??

The 6mm T&E runs about 12m from the house CU to the garage CU. The 16 amp run (2.5mm T&E) then runs about 4m from the CU to the socket. From the socket to the saw is yet to be determined. Am i running close to a limit or am i ok? I need to sort the workshop out properly!

 

[Sidewinder]

What other loads are running off these cables?
A 32 will only be fine if you don't care which one trips in the event of a fault.
You need to look at selectivity and inconvenience, as well as your own safety.

 

[Sidewinder]

By the way, why would you have not expected my comment?
That's not a nasty dig, I would like to understand please.

 

[rorie]

OK, I used to do warranty repairs for Axminster.
So I know their kit quite well.
First, as BS asks we must know the motor rating plate details.
Then we need to know the cable sizes and lengths back to the DNO fuse, that way voltage drops can be assessed to be sure that the starting load of the motor is not "pulling" the supply voltage so low that it is below the value at which the "NVR" (I hate that term!) will not retain.

I cannot easily get to the motor rating plate as i have side tables and sliding tables bolted all over the place! But looking up the spec it states 2.2 kW motor, 230v 1ph.

 

[brightspark]

I cannot easily get to the motor rating plate as i have side tables and sliding tables bolted all over the place! But looking up the spec it states 2.2 kW motor, 230v 1ph.

3 hp about 12 amp full load running amps and about 50 on start up inrush .if u have a new nvr switch just fit it and see if it cures the problem

 

[Sidewinder]

Full load current from the motor rating plate please as this is the only way to assess, motor starting current thus instantaneous volt drop during the starting of the motor, and then it's only a guess without additional information which only the machine & motor designers have, unless you undertake power analysis on the motor inrush starting current.

 

[rorie]

By the way, why would you have not expected my comment?
That's not a nasty dig, I would like to understand please.

Ah, perhaps i misunderstood….. or was unclear as i am now reading Brightsparks comments differently too. i thought you were saying the RCD in the garage must be a high value than the MCB upstream in the house? The RCD in the garage is 63amp, and the MCBs downstream are all lower values (32amp, 6amp etc).

I would have expected the MCB in the house to be a higher value than the RCD in the garage…. I think i am getting very confused now! Sorry!

 

[rorie]

Full load current from the motor rating plate please as this is the only way to assess, motor starting current thus instantaneous volt drop during the starting of the motor, and then it's only a guess without additional information which only the machine & motor designers have, unless you undertake power analysis on the motor inrush starting current.

Right, i'll get to that tomorrow and report back.

3 hp about 12 amp full load running amps and about 50 on start up inrush .if u have a new nvr switch just fit it and see if it cures the problem

So you think the current set up as is (with the wire fuse in the house) shouldn't be causing the problem?

I must say folks, your all being extremely helpful - thanks! I joined a sparks forum and what a waste of time that was! I never though of trying here until i found an old post.

 

[Sidewinder]

An RCD has NO overcurrent protection so in the event of an overcurrent it MUST be protected by upstream devices.

Now you have a 32A MCB in the garage, say a B curve, you protect this by a B32 in the house, in the event of a 100A fault current which will trip first?

 

[Sidewinder]

Right, i'll get to that tomorrow and report back.



So you think the current set up as is (with the wire fuse in the house) shouldn't be causing the problem?

I must say folks, your all being extremely helpful - thanks! I joined a sparks forum and what a waste of time that was! I never though of trying here until i found an old post.

Which sparks forum, not mine I suspect!

 

[brightspark]

Ah, perhaps i misunderstood….. or was unclear as i am now reading Brightsparks comments differently too. i thought you were saying the RCD in the garage must be a high value than the MCB upstream in the house? The RCD in the garage is 63amp, and the MCBs downstream are all lower values (32amp, 6amp etc).

I would have expected the MCB in the house to be a higher value than the RCD in the garage…. I think i am getting very confused now! Sorry!

mcb at supply in house 32 amp mcb feeding saw in garrage 16 amp

 

[brightspark]

just change the nv r switch if u have one and see what happens the cable length and and core size seem ok

 

[rorie]

Perfect! I understand now!

So in the garage unit i'll install the type c 16 amp MCB in the spare slot and run a 2.5mm T&E to the 16 amp socket (as i already have the kit to do it). I'll also install the new NVR.

If i still have problems i'll (and by 'i', i mean a sparky if i can ever get him to come round!) change out the CU in the house and put in a DP switch with 32 amp MCB.

And all will be sorted!

Thanks very much folks! Much appreciated!


And FYI - it was "http://www.electriciansforums.co.uk". They actually closed my topic as i "obviously" didn't know what i was talking about and accused me of making up my electricians existence, so decided that it was too dangerous to share their knowledge with me. least helpful forum yet!