TT supply advice required

[supermotodaz]

Hi
I,ve been away from the domestic scene for a while and would apreciate some advice.
Been asked to check a supply already installed to make sure it meets the requirements.
Its a TT supply, outside in an enclosure is the main cutout 100a, meter and then seperate 100a mainswitch, from here under the house runs a 16mm 2 core swa, aprox 15m run which feeds a 63a rcd (not checked the ma rating yet on this) in its on enclosure, think this was done to give a metal casing to gland off swa cable into then from this in 25mm tails to a distboard with 100a mainswitch. I,m assuming i need to up the swa to a 25mm and change 63a rcd or up rating and use a time delay type. What do you guys advise.
Cheer,s
Daz

 

[sjm]

Where's the earth rod? I think that a time delay RCD should be at the main cutout end (origin of the supply) as should the main earth.

 

[supermotodaz]

Where's the earth rod? I think that a time delay RCD should be at the main cutout end (origin of the supply) as should the main earth.

Cheer,s for reply, earth rod is in and earth run from main incomer position to earth rod is only a metre distance, not sure if it matters where along that swa or rather which end it go,s as it will do the same job anyway.

 

[sjm]

The supply from the main incomer to the cu is a distribution circuit from a TT supply and therefore must have RCD protection at the origin. Armour of swa should be earthed at the supply end.

Cheers

 

[La Poste]

The supply from the main incomer to the cu is a distribution circuit from a TT supply and therefore must have RCD protection at the origin. Armour of swa should be earthed at the supply end.
Cheers

Does this mean it must be RCD's at the suppliers end or at the incomer?

 

[vambo]

If the main fuse is 63A the swa is fine, anything over this you need to up the swa to 25mm. Just because the main incomer fuse carrier say's 100A on it doesnt mean it has a 100A fuse in it.

 

[supermotodaz]

If the main fuse is 63A the swa is fine, anything over this you need to up the swa to 25mm. Just because the main incomer fuse carrier say's 100A on it doesnt mean it has a 100A fuse in it.

I,ll check the fuse size, all i can find in the onsite guide is ref 514.3 which states minuim cable size should be 25mm ,i cannot find further info on this so i assumed that the swa must be upgraded anyway as in theory it is now the meter tails only 15 m in length and of an swa construction.

 

[supermotodaz]

The supply from the main incomer to the cu is a distribution circuit from a TT supply and therefore must have RCD protection at the origin. Armour of swa should be earthed at the supply end.

Cheers

Hi
Should this rcd at the origin by of a time delay type of at a different ma rating from the main distboard.

 

[sjm]

In order to obtain discrimination I would fit a 100ma S(time delay) type at origin. Meter tails should only be 3-4 mtrs in length so your swa will have to be a distribution circuit and therefore requires a disconnection time of max 5 seconds. If you can fuse the distribution circuit at 63amps you can keep the 16mm no need for 25mm as this only applies to meter tails. However if the MET is at the origin you will have to install a main protective bonding conductor min for TT is 6mm.

Hope this helps

 

[supermotodaz]

In order to obtain discrimination I would fit a 100ma S(time delay) type at origin. Meter tails should only be 3-4 mtrs in length so your swa will have to be a distribution circuit and therefore requires a disconnection time of max 5 seconds. If you can fuse the distribution circuit at 63amps you can keep the 16mm no need for 25mm as this only applies to meter tails. However if the MET is at the origin you will have to install a main protective bonding conductor min for TT is 6mm.

Hope this helps

Thanks for your reply.
Providing the property is not going to draw a 63 amp load, can i replace the main cut fuse with a 63 if it is larger already or is that a definate no no as its the suppliers equipment. I don,t know if you would class this as the MET but what the guy has done is that he,s run a 16mm from the earth rod to the 100a metal enclosure of the 100a main switch feeding the swa (this is only a 1m length) and he has connected the 16mm onto the banjo of the 2 core armoured, so the swa would be your main earth to the db.