Discuss Tails - metal board - TT system in the UK Electrical Forum area at ElectriciansForums.net
Will ring the NICEIC techline tomorrow and see what fob offs they can spin me. Attended a freebee Hager 'technical seminar/sales pitch' tonight through my wholesaler. The speaker couldn't give a proper answer to the question. Does anyone know of a specific double insulated/reinforced insulation grade glanding system that can accomodate tails?
or measure must be taken to minimise the chance of a fault to the metal case. This would mean keeping tails sheathed all the way to the terminals....tails kept as short as possible,and most importantly an insulated bush and some form of cable clamp to prevent any movement of the tails.
I'm not sure where the bit about the new amendment is relevant. If a metal board is used on a TT now the measures I stated in post 2 apply,it will be no different under the amendment.
It's all well and good ensuring that the tails are kept well secure, insulated and sheathed, but what about the busbar and neutral bar?
IMHO, the only two ways to ensure adequate earth fault protection of a metal DB on a TT system are to either guarantee TN values or fit an up front s-type.
Oh, and the up front s-type will have to be housed in plastic.
This reg just makes perfect sense! LOL
Assuming the metal DB has an RCD main switch,or was a '17th' twin RCD then the busbar(s) and neutrals would be on the RCD side and the metal case would be protected from a fault via those.
I merely stated that the requirements under the new amendment for a metal DB on a TT will be no different to those that are already in place as far as I can see.
I know what your saying - its always been an issue where M/C CUs and TT systems are concerned, I think the point is that issue becomes all the more prevalent post June 30th 2015 when we will be forced to use M/C CUs as standard. So the manufacturers are going to have to step up and make contractors aware of the options, because at the moment all I'm getting conflicting opinions. NICEIC have just said to me that the only real option/solution is using suitable class 2 glands and reducing the likely hood of fault between the tails and the metal case using cable clamps etc.Assuming the metal DB has an RCD main switch,or was a '17th' twin RCD then the busbar(s) and neutrals would be on the RCD side and the metal case would be protected from a fault via those.
I merely stated that the requirements under the new amendment for a metal DB on a TT will be no different to those that are already in place as far as I can see.
NICEIC have just said to me that the only real option/solution is using suitable class 2 glands and reducing the likely hood of fault between the tails and the metal case using cable clamps etc.
But how do you get over the fact the RCD will have to be housed in a metal enclosure?And they would be very very wrong!
As I said earlier the only real option of providing earth fault protection to a metal DB on a TT system where TN Ze values cannot be guaranteed is by fitting an s-type up front.
But how do you get over the fact the RCD will have to be housed in a metal enclosure?
That's interesting I didn't know that. Bit silly though because to all intents & purposes it has all the fire risks of a DB; Tail terminations carrying the installations full load, a device which incorporates mechanical and electronic components and contacts - all capable of catastrophic failure and subsequent combustion?It won't, as it would be a single RCD in an enclosure it wouldn't be a distribution board, therefore it wont be subject to the requirements of that regulation.
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