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Topic Title: Service cable/main overloaded ?
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Created On: 10 October 2013 10:34 AM
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 10 October 2013 10:34 AM
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broadgage

Posts: 1261
Joined: 07 August 2007

TNC-S service, 3 phase cut out serving a farm, fitted with 300 amp fuses.
DNO transformer nearby, capacity unknown.

Looped out of the line side of the cut out is a service cable for a 3 phase domestic supply fitted with 60 amp fuses.

The loading is very substantial and the cable between the transformer and the first cut out gets alarmingly hot, as does the transformer.
It would appear that the service cable between the transformer and the farm belongs to the DNO, and has existed for years. The new cable to supply a new house has been looped off this.

I suspect that the transformer and DNO cable were already marginal and may have been pushed over the edge by the addition of the 60 amp domestic service.

Most of the load is off peak with both services probably at least 90% loaded for some hours every night.

Measured surface temperatures are about 75 degrees for the cable and about 90 degrees for the transformer.
And that at only 320 amps actual measured load on both services.
I hate to think what would happen if both services were 100% loaded.

The main loads are an electric crop drying installation, bulk water heating, and off peak central heating.

Do you think that the DNO will do anything before it blows up !
Have reported it and got no where.
 10 October 2013 10:44 AM
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AJJewsbury

Posts: 11216
Joined: 13 August 2003

Measured surface temperatures are about 75 degrees for the cable

Might that be acceptable for say a 90-degree cable?

- Andy.
 10 October 2013 11:00 AM
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perspicacious

Posts: 7104
Joined: 18 April 2006

"Do you think that the DNO will do anything before it blows up !
Have reported it and got no where."


It sounds as if it isn't the DNO's problem but if it does "blow up", they could simply look up the farmers ASC and the MD recorded and suggest that the farmer comes clean and requests a supply increase (just because there are 300 A fuses fitted doesn't mean that the ASC is ~200 kVA) and on receipt of his cheque, they'll program the upgrade

Commonly known as undeclared ASC load creep.........

Regards

BOD
 10 October 2013 12:24 PM
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broadgage

Posts: 1261
Joined: 07 August 2007

Originally posted by: AJJewsbury

Measured surface temperatures are about 75 degrees for the cable

Might that be acceptable for say a 90-degree cable?
- Andy.


Maybe, just.
But the qouted 90 degree figure is for conductor temperature IIRC not surface temperature of the sheath.
And this was on a cold day and at only about 90% load.
 10 October 2013 12:31 PM
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broadgage

Posts: 1261
Joined: 07 August 2007

Originally posted by: perspicacious

"Do you think that the DNO will do anything before it blows up !

Have reported it and got no where."




It sounds as if it isn't the DNO's problem but if it does "blow up", they could simply look up the farmers ASC and the MD recorded and suggest that the farmer comes clean and requests a supply increase (just because there are 300 A fuses fitted doesn't mean that the ASC is ~200 kVA) and on receipt of his cheque, they'll program the upgrade



Commonly known as undeclared ASC load creep.........



Regards



BOD


Not this time !
I filled in the original request which listed
Grain dryer at 150 KVA
Water boiler at 27KVA
Lighting and small power 20 KVA (after diversity)

I was not innvolved in the 3 phase 60 amp service to the house, but the application did refer to an 18 KW 3 phase central heating unit, plus the usual lighting and small power loads.
 10 October 2013 10:22 PM
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slittle

Posts: 3441
Joined: 22 November 2007

I know of a building which used to be a fire and rescue service headquarters. The incomer was "warm" quite a few years ago and has continued to get hotter, never been a problem yet.

Just make sure (if you can) that the heat isn't travelling down the cable from a loose connection in the cutout. I've seen that happen more than once.

Stu
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