16 amp help wanted!!

[jonny boy]

I'll have a look, two mins.

 

[jonny boy]

Davy, I have the installation schedule with me and there's a part that say's Ze at origin and the spark has written down .07 ohms. Does this help?

jon.

 

[davy_owen_88]

With a Ze that low, and a circuit length as short as yours, you should have no problem upgrading to a C-type breaker. Sorry for dragging this out, it's just that most people have no idea what calculations go into determining these things and the possible outcome of a poorly designed or modified circuit.

 

[davy_owen_88]

I just had a thought, when you said 2m from CU to 16A supply, is the CU you are measuring from the main CU or a submain fed from another CU?

 

[jonny boy]

Davy, I feel quite confident enough to fit the class C breaker myself and alway's ensure that it's isolated first. I know that a qualified electrician should do this but I feel it's unnessesary to pay for one when I can do it myself. I don't expect you to recommend me doing it myself but but i'm sure your getting the jist of what i'm saying!

Thanks for your help, much appreciated.

jonathan.

 

[jonny boy]

There's only one C/U in the house which is located in the garage and the outlet for the saw is about 1.75 metre's below it.

jon.

 

[davy_owen_88]

I have absolutely no problem with you physically changing the MCB yourself. The need for a professional comes with determining whether you should be changing it and if it is indeed safe for you to do so. In your case, with the low Ze and short circuit length your Zs is within limits so assuming all connections are tight you can go right ahead and change it.

 

[jonny boy]

Thanks for your help in this matter Davy. I'll let you know how the class C mcb performs.

I would just like to point out to other forum members that this thread is not a guide on how to connect your machines, it is just a discussion on a problem i'm having with my saw and any electrical work should be carried out by a competent electrician.

thanks,
jonathan.

 

[devonwoody]

Very interesting information above.
Before the latest regs came in, someone fitted a 6mm cable from my C/U to the garage around 12 mtrs. long to another c/u. the second c/u has a 32 amp breaker. says nb32
My earth is connected via the armour cable that comes into our property (1963 era)

The earth has been checked a couple of times (by the washing machine repairer, who says OK) in the property.

Any advice gratefully received.

 

[seaco]

Ok straight off the bat I know nothing about electrics but I do have a Unisaw so I've had a look at the fuses the electrician fitted and they are as follows:

In the shed the fuse for the saw says:

NB 30
30A Type 2

In the house the shed has it's own fuse and says:

Square D

SQO

132EC6

C32

BS EN 60898


Now this may be of no help at all but you must admit I am trying...

 

[jonny boy]

Lee,

Does the motor on your unisaw say 12.4 amps? If so, it will be the same motor as in my saw and it seems you have a 32 amp breaker fitted to run it. I have just bought a 16 amp class C breaker from screwfix this morning. I had the choice of either a 6Ka or a 10Ka and I bought the 10Ka. Does anyone know if this is ok?

thanks,
jonathan.

 

[davy_owen_88]

The kA rating is the short circuit breaking capacity. This is the maximum current that the MCB can break if the circuit develops a live-neutral fault.

The PFC (prospective fault current) should be noted on your EIC near to where you read the Ze last night. If your PFC is higher than the breaking capacity it means that during a fault the 'electricity' can just arc across the contacts and continue to flow. It is generally of little concern though as a service fuse with a high breaking capacity backs up the MCB's in a consumer unit.

 

[jonny boy]

Welcome back Davy,
How would one find the prospective fault current and are you basically saying that the 10Ka breaker i've bought wont make any difference and it's OK?

jonathan.

 

[davy_owen_88]

The PFC should be written on the certificate near the Ze reading.

It doesn't really make any difference if your PFC is higher than the breaking capacity of the MCB but if you can get one which exceeds the PFC then you should. You don't want your main fuse blowing when the MCB could have done the same job without knocking out your entire house. :wink:

But yes, the MCB you have is fine, you only need to worry if your PFC is higher than the breaking capacity of your main fuse...

 

[jonny boy]

I'll have a look,
2 mins

 

[jonny boy]

Below the Ze at origin it has PSSC but there is nothing written down, the spark has left it blank.

jon.

 

[davy_owen_88]

Tut tut :roll: All boxes for supply characteristics should be filled in on a EIC...

On the EIC there should be a section called 'Characteristics of primary overcurrent pretective device'. What does it say there?

 

[jonny boy]

there is a heading that say's overcurrent device then next to that it say's circuit conductors then next to that it say's test results. Is this it?

 

[davy_owen_88]

The info should be recorded before that but some sparks will enter the meter tails and the main service fuse on the first line of the schedule of test results.

The characteristics of primary overcurrent protective devices should be on the same page as the Ze and PSCC.

 

[jonny boy]

The chart has a list of circuits down the left hand side ie. lights, sockets, cooker etc, and then from left to right it has boxes that are filled in by the spark which are, no. of points, type, rating, short circuit capacity, live, CPC, continuity, insulation, resistance, earth loop impedance, functional testing, polarity and remarks.
If I knew how to, i'd scan the thing so you could see it yorself!

jon.