Maximum cable length

[Disk]

I would be grateful for some help re the following: Where the floor area served by a domestic power ring main falls within the 100sqm max, does the recommended max 60m cable length refer to the total cable ring length from and back to Fuse board or half of the overall length because of the effect of the ring?

 

[Big_Spark]

The total recommended length of a ring circuit should not exceed 60 meters.


In a domestic premises this should never be an issue unless you live in a stately home

 

[securespark]

FWL, not disputing you at all, where does that 60m come from? I thought 100m2 was only constraint??

 

[Disk]

FWL - thanks for reply BUT: No stateley home, but when I do the calcs I keep coming up with in excess of 70m.
Ground floor sockets supplied from 1st floor. My figures are only approx but if the 60m rule should never be a problem I cannot understand why my humble abode should have figures anywhere near it.
Vertical : socket to ceiling 2.3m * 7 sockets * 2 = 32m
Horizontal: length of house from FB and back - 2* 9m = 18m
front to back of house for 3 sockets * 3m * 2 = 18m
front to back of house for 1 socket * 2m *2 = 4m
Grand total = 72m

 

[Big_Spark]

FWL, not disputing you at all, where does that 60m come from? I thought 100m2 was only constraint??

The 60m is the maximum recommended length for a ring main from one end to the other..HOWEVER this is only an arbitary recommendation, not a real one, the only one you need truly concern yourself with is the 100 sqm one.

 

[Big_Spark]

FWL - thanks for reply BUT: No stateley home, but when I do the calcs I keep coming up with in excess of 70m.
Ground floor sockets supplied from 1st floor. My figures are only approx but if the 60m rule should never be a problem I cannot understand why my humble abode should have figures anywhere near it.
Vertical : socket to ceiling 2.3m * 7 sockets * 2 = 32m
Horizontal: length of house from FB and back - 2* 9m = 18m
front to back of house for 3 sockets * 3m * 2 = 18m
front to back of house for 1 socket * 2m *2 = 4m
Grand total = 72m

One question, why are you going UP the wall, instead of under the floor boards downstairs?

Secondly, are you seperating the Kitchen and other rooms ring mains into two seperate circuits?

 

[Disk]

FWL- Thanks again for your comments.
1, It is a ground floor circuit but the ground floor is concrete so the sockets are fed down from the first floor.

2. Short answer No BUT - the kitchen is part of the same ring as the rest of the ground floor but I have the heavy demand kitchen type items in a Utility room which is on a separate circuit. The main demand on the circuit in question is a kettle, extract fan, TV and HiFi which I am sure will not cause any problem.
My concern is that a future buyer (not anticipated for many years yet) may decide to reorganise and change the ground floor use.

 

[Big_Spark]

Disk, it is always a good idea to put the kitchen on a seperate ring. It is good to see that your utility room has this, but kitchens should have them as well.

I would assume that your fridge, a freezer and a Microwave populate your kitchen....always good to have these items on a circuit seperate from electronic equipment..especially fridges and freezers due to the switching of the compressors.

Remeber an 850W Microwave will consume around 1 to 1.1kW, if it is a fan oven as well, this could rise to about 1.5kW.

If you have a 2.5 or 3kW kettle, add the other items and you can start to see that there is more load there than you may think.

 

[BR]

Generally in houses I would put the following socket circuits
1 Kitchen
2. Utility
3. Sitting room
4. Rest of house

I know this seems like a large circuit for the 'rest of house' but in practice it is the circuit, which has, the least load placed upon it.

 

[Big_Spark]

I concur with BR on this..

 

[il78]

"Sitting room"......I must be common

What about (for the common people):

1)Kitchen (RCD)(this includes the utility room, but excludes the butlers quarters)
2)Upstairs Sockets
3)Downstairs Sockets (RCD)

 

[Big_Spark]

Better scenario for this situation would be.

1: Kitchen......32A 100mA RCBO
2: Utility Rm...32A 100mA RCBO
3: Down Ring..32A Type B MCB
4: Up Ring......32A Type B MCB
5: Down Light. 6A Type B MCB
6: Up Lights.... 6A Type B MCB

I would not put 30mA RCBO's on the two circuits listed as these can suffer nuisance tripping from Fridges, Freezers, washing Mashines etc.

I can't tell you how many call-outs we have attended due to this problem

 

[securespark]

FWL

But what about protecting those outlets likely to supply equipment outdoors?

100mA no good is it??

 

[il78]

This was mentioned before in another post.....

"When designing, external sockets will be accounted for" something like that was said......

But it does say all sockets reasonably expected.......and I would consider all.....

 

[Big_Spark]

FWL

But what about protecting those outlets likely to supply equipment outdoors?

100mA no good is it??

The simple way around that thorny issue has two solutions.

1: Install a dedicated MK Seal Range range RCD protected IPX4 socket outside for this use, it can be on the ring, but I would advocate a seperate radial circuit for it protected by a 16A Type 2 MCB.

2: Any socket on the downstairs or kitchen rings that will likely be used for external supplies make into internal use RCD sockets.

My personal preference is always no 1.