Stroma Certification Scheme stroma assessment this week

[phil lancaster]

I put the 20A as the max demand in the shed was only 11.25A so I thought that 20A would be adequate with a 6A for the light and 16A for the socket
phil

 

[Gavin John Hyde]

You have designed and installed it so you should know how to size the MCB through calculation.

I agree, hate to be harsh but your assessor tomorrow is going to ask these questions of yourself, so go back to your design calcs and look at the load and any diversity calcs etc then decide on what you think you need.
Its better you come to your own decision and can then explain the reasoning why and how you come to them. the assessor will then be more forgiving of any errors if you can show reasons and at least a decent effort. its far more than many do and they just put bits together and if it works then good. no design or initial verification whatsoever.

 

[westward10]

Well I hate to tell you yes he is I will be telling him what I think tomorrow afternoon the sod what size mcb do you think I should replace the rcdo with the cable is 4mm 2 core swa
phil

Is it surface fixed, buried in the ground?

 

[phil lancaster]

#
buried its the 20A rcd to feed in the house to the 40A main switch in the shed cant see any diff to a 60A dno fuse and 100A main switch the load is very low as it will only be supplying the Lawn mower that is if it ever stops raining and 1x10watt led bulb but I allowed 100w for the light as it states in regs
phil

 

[Ian1981]

4mm swa Clipped direct 38 amps, ref method D buried will carry 37 amps.
However as it's buried there is a 0.9 correction factor to be used and if you can be bothered there's depth to consider, ground temp, is it in a duct and soil thermal resistivity.
I'd stick with your 20 amp mcb as it's very unlikely to be overloaded with just one light and one socket and you will never achieve descent discrimination with your 16 amp mcb in the shed with the supply mcb anyway

 

[phil lancaster]

hi thanks for your opinion I took into account the points you raised inc voltage drop I have all the calculation for him to look over just with the advise and info I was getting I started to doubt myself as my head is battered getting things ready as it has been a very quick turn around from phoning stroma and the as visit has only been a week
thanks for all you help everyone

 

[Taylortwocities]

#
buried its the 20A rcd to feed in the house to the 40A main switch in the shed cant see any diff to a 60A dno fuse and 100A main switch

Phil, I think that you are misunderstanding something. The 40A marking on a 30mA RCD does NOT relate to a tripping current. The 40A relates to the amount of current that the switch contacts in the RCD can handle. The RCD does not have any over current protection.
In the same way, a 100A main switch is just a switch that had contacts that can handle currents up to 100A. That device also provides no over current protection.

Quite honestly your design is not good. If you only have a light and a socket in the outbuilding, you don't need a CU out there. Just the RCBO in the house and a simple switched FCU with a 3A fuse in it for the lights.

But you are where you are now. As above, tske that RCBO out at the house end and put in an MCB big enough to provide discrimination with the 16A MCB in the outbuilding. You need to size it correctly for the size of the SWA cable.

I suggest you get some really nice biscuits for the STROMA guy. You are going to need him on your side!

 

[Ian1981]

Phil, I think that you are misunderstanding something. The 40A marking on a 30mA RCD does NOT relate to a tripping current. The 40A relates to the amount of current that the switch contacts in the RCD can handle. The RCD does not have any over current protection.
In the same way, a 100A main switch is just a switch that had contacts that can handle currents up to 100A. That device also provides no over current protection.

Quite honestly your design is not good. If you only have a light and a socket in the outbuilding, you don't need a CU out there. Just the RCBO in the house and a simple switched FCU with a 3A fuse in it for the lights.

But you are where you are now. As above, tske that RCBO out at the house end and put in an MCB big enough to provide discrimination with the 16A MCB in the outbuilding. You need to size it correctly for the size of the SWA cable.

I suggest you get some really nice biscuits for the STROMA guy. You are going to need him on your side!

As it's 4mm supplying the garage he's got no chance of achieving any discrimination with an appropriate OCPD (mcb type anyway)and probably won't achieve it with the 6amp mcb either

 

[Taylortwocities]

Yes I know, I just didn't want to rain too much on his parade.

 

[Taylortwocities]

Complaints form

 

[Gavin John Hyde]

Anybody know if the OP passed the Stroma Assessment....

 

[westward10]

Anybody know if the OP passed the Stroma Assessment....

Hopefully he will update us however it went.