Upgrading a cunsumer unit to RCD status

[EFLImpudence]

Not sure why the lever connector page isn't showing

There's a full stop at the end.

 

[ricicle]

Most consumer units will only take the single pole switching RCBO's which are permitted with TN supplies but not with a TT supply with the latter all pole switching is required.

Unless I'm missing something, I don't think that is necessarily strictly true, since I'm not aware of any regulation which requires double-pole protective devices in TT installations (the only requirement of which I'm aware being that 'isolation' be DP in TT installations).

As long as the main switch is DP (which I don't think there are many that aren't) then SP RCBOs are fine on a TT system.

 

[JohnW2]

Most consumer units will only take the single pole switching RCBO's which are permitted with TN supplies but not with a TT supply with the latter all pole switching is required.

Unless I'm missing something, I don't think that is necessarily strictly true, since I'm not aware of any regulation which requires double-pole protective devices in TT installations (the only requirement of which I'm aware being that 'isolation' be DP in TT installations).

As long as the main switch is DP (which I don't think there are many that aren't) then SP RCBOs are fine on a TT system.

Exactly. However, as I went on to say, there is a potential issue (regs-wise) if there is an up-front TD RCD - since an N-E fault on a circuit protected by a SP RCBO will then take out the whole installation.

Kind Regards, John

 

[Rogeranerley]

Thanks again for all your comments. As the CU has DP switches for the main and RDC sides, it seems my house is on the TT.

I'd also be grateful for your clarification on the power supply to the illuminated/shaver cabinet. This is stated to require a supply at 5a, whereas the MCB (and a potential RCBO) carrying the lighting circuit is at 6a. Does this mean the line to the cabinet has to be run through a 5a spur?

In case its useful to anyone else, Hager have advised that their RCBO Type B SP ADN Range has the same profile as their MTN MCB range, except with a height of 115mm compared with the MTN at 85mm. I've found that the MTB profile comfortably fits into my 20 year old Hager IECOS 66-6H Consumer Unit, the original MCBs being marked M6 type B, M32 type B etc.

 

[ban-all-sheds]

As the CU has DP switches for the main and RDC sides, it seems my house is on the TT.

Sorry - I don't follow that.

 

[slippyr4]

Sorry - I don't follow that.

Not to worry, I don't think Rogeranerley does either

 

[Rogeranerley]

slippyr4's right....I don't really understand this TT/TN stuff.

I'd be grateful if someone could clarify for me whether I need to fuse down to 5a for the shower room cabinet from the 6a lighting circuit.

Thanks again everyone.

 

[Taylortwocities]

You can run it off the (6amp) lighting circuit without having to insert a 5amp fuse.

In the event of a fault, the 6amp MCB will trip a long time before the 5amp fuse would blow.

 

[ban-all-sheds]

slippyr4's right....I don't really understand this TT/TN stuff.

Your installation is (you hope) earthed.

At the substation, the neutral point of the transformer is earthed.

What happens between there, and you, is described by the TN-S etc designations.

TN-S - the earth from the substation transformer is taken to you as a separate (usually the sheath of the supply cable).

TN-C-S - the earth is combined with the neutral (which is earthed at the substation anyway), and then at the service head in your house turned into a separate earth for your circuits.

TT - no earth is provided by the supplier, you have an earth rod in the ground outside.

 

[RF Lighting]

TT - no earth is provided by the supplier, you have an earth rod in the ground outside.

TT - no earth is provided by the supplier, you should have an earth rod in the ground outside.

 

[ban-all-sheds]