Existing supply

[waynelester]

HI,IM AFTER A BIT OF ADVICE.Im ABOUT TO INSTALL A NEW CONSUMER UNIT BUT AM A LITTLE CONFUSED TRYING TO IDENTIFY THE SYSTEM,IE TNS OR TNCS.THE MAIN TAILS ARE 16MM AND THE EARTHING CONDUCTOR IS CONNECTED TO THE SIDE OF THE FUSE UNIT BY A BRASS SCREW CONNECTOR AND THE SIZE IS VERY SMALL PROBABLY ABOUT 4MM AND THE SAME FOR THE MAIN BONDING TO THE GAS AND WATER.THE CONSUMER UNIT IS AN OLD REWIRABLE TYPE.WOULD I NEED TO UPRATE THE EARTH CONDUCTOR AND MAIN BONDING. THANKS

 

[Amp David]

Do a Ze test and that'll give you an idea of your earting arrangement.

Upgrade the bonding and earth. Its all in the BRB, nice and easy stuff really.Is this for your scheme assessment or a bit do it on the cheap DIY?

 

[IQ Electrical]

Have a read of this: http://www.esc.org.uk/pdfs/business-and-community/electrical-industry/BPG1v2_web.pdf

It won't help you to identify the earthing system but it will explain your responsibilities regarding earthing and bonding.

 

[waynelester]

do a ze test and that'll give you an idea of your earting arrangement.

Upgrade the bonding and earth. Its all in the brb, nice and easy stuff really.is this for your scheme assessment or a bit do it on the cheap diy?

thanks,yes i have assessment in couple of weeks andthis is a job iv been looking at doing i done a ze test on a tns and got a low reading of 1.2.i thought that tns systems you could physically see the earth conection on the sheath of the incoming cable

 

[Amp David]

Ok no worries. First problem you have is that on a tns earthing arrangement, the max Ze should be 0.8Ω, so you are a bit high.

tns earths do usually have a connection of some kind sweated onto the main supply cable.

 

[IQ Electrical]

thanks,yes i have assessment in couple of weeks andthis is a job iv been looking at doing i done a ze test on a tns and got a low reading of 1.2.i thought that tns systems you could physically see the earth conection on the sheath of the incoming cable

Do you mean 0.12 ?

 

[waynelester]

Yes sorry 0.12

 

[cagedanimal2010]

if .12 i would suggest its a tncs

danny

 

[Deleted member 19807]

one option is that it may have been a TT that has been changed to a tnc-s but without the bonding upgrading, are there any lables talking about "PME" in the meter cab? There should be if its official but thats not always the case, if it looks at all diy tnc-s and as this is for an assesment i would call the dno and ask them what earthing arrangment they think they have there (if they know).

 

[brucelee]

it sounds like a tn-c-s if the earthing is connected to the side of the cut out fuse by a brass terminal connection this is where the earth is linked to neutral in the supply side from the cutout back to transformer eg star point
if it was tn-s it would be connected to the metallic sheathing of the armour and would have to be lower than 0.8ohm
and as you have got .12 thats well within the 0.35ohm max for a tn-c-s

but upgrade the earthing conductor to 16mm
the main protective bonding to 10mm
and the tails have to be upgraded to 25mm

good luck with your assessment mate

 

[waynelester]

Hi thanks,do the tails have to be 25mm even if supply fuse is 80amps or less and what if it was tns

 

[Deleted member 19807]

Hi thanks,do the tails have to be 25mm even if supply fuse is 80amps or less and what if it was tns

no, for a 80A supply fuse you can use 16mm. As with all cables you install the fuse rating must be rated at less then the current carrying capacity of the cable, taking into account de-rating factors.

 

[SirKit Breaker]

HI,IM AFTER A BIT OF ADVICE.Im ABOUT TO INSTALL A NEW CONSUMER UNIT BUT AM A LITTLE CONFUSED TRYING TO IDENTIFY THE SYSTEM,IE TNS OR TNCS.THE MAIN TAILS ARE 16MM AND THE EARTHING CONDUCTOR IS CONNECTED TO THE SIDE OF THE FUSE UNIT BY A BRASS SCREW CONNECTOR AND THE SIZE IS VERY SMALL PROBABLY ABOUT 4MM AND THE SAME FOR THE MAIN BONDING TO THE GAS AND WATER.THE CONSUMER UNIT IS AN OLD REWIRABLE TYPE.WOULD I NEED TO UPRATE THE EARTH CONDUCTOR AND MAIN BONDING. THANKS

Wayne,

Firstly please don't shout, use lower case for your post's not capitals.

Secondly, i have just read your post through a couple of times. If i were in your shoes then i would be giving serious consideration to the prospect of having a Part p scheme assessment. You are asking things that you should really know off the top of your head to stand even half a chance of success, and the question regarding the earthing arrangement of your supply, you should be able to find out using the correct books, and test equipment. Your supply fuse rating determines your supply tails CSA, and this in turn determines the size of your main earth conductor, which determines bonding sizes and so on. You can't take the fuse out, so you must work on the worst case scenario. fit 25mm tails, and then the rest is determined from this. I wont tell you what the sizes are, because if you dont know, then you need to go and look and find out. Any assessor will expect you to know the basics, and if you dont then you would be better off spending your money more wisely.

Cheers..........Howard