Domestic DB

[Phaze-3]

Hi Guys,

Take a look at the picture below. (you may have to turn your head as i couldn't work out how to rotate it it).
As you can see, the DB has seen better days so i am going to replace it with a nice new one with plenty of ways.

I don't get to involved with domestic work as i really only work with industrial installations and bigger stuff. Few questions you guys hopefully will be able to help me with. I will just add that this is a TT System to this house.

1) How far does does the main intake and DB need to be away from the Gas Meter?(As you can see, it is pretty close)

2) I done a Ze on the existing board and was getting a silly reading! Do i need to be looking at installing a new earth rod? If so where is the best place to put it?

3) Choosing a new DB. I was thinking of getting the usual 2 x RCD split boards. Now do i need an RCD Main Switch to feed the Split board (if that makes sense). and if i do does that main switch ideally need to be 100ma?

or

4) can i put a normal DB in with a 100ma main switch and RCBO's to feed each circuit.

I've been a spark for 14years but only ever work on industrial installations and dont know that much about the domestic side of things these days. There are just a few little question im just not sure about when it comes to some of the regs that are involved in domestic installations.

Cheers Guys


Steve

 

[telectrix]

recommended min. distance from gas meter is 6". bang in screwed rods joined together at least 3ft. from the outside wall of the building so as to avoid all the builder's rubble. an up front 100mA s type RCD would also serve as an isolator for the DB. i would fit an 8 way DB with RCBOs if customer will pay.

 

[Jay Sparks]

Hi Phaze 3,

What was your Ze reading? You may need to add another, longer rod. As for the were to put it, only you will know what the condition of the ground is were you are.

You will need an up front 100mA time delayed rcd, then your cu with 2 x 30mA rcd or even better, fit all rcbo's.

I havent got my onsite guide with me but of top of my head, the db needs to be about 150mm from other services.

Jay



Damn it tel, do you not go to work????lol

 

[telectrix]

been, done, come home.

 

[Jay Sparks]

Ha Ha, lucky for some. I havent even been today and you still beat me to the post.lol

 

[telectrix]

did a CU change saturday. just a couple of hours today live testing.

 

[PEM]

How close is the existing earth rod to the house? Under the eaves tends to result in dry ground and poor contact. I find a house for half an hour or so can help.

 

[Silly Sausage]

I'd mount the new CU on a stand off board to the right of the meter board.
That way, you can run the cables into the back of the CU and won't comprise the IP rating of the unit by hacking holes into any of its sides. (IP4X top, 2X elsewhere)



Can someone explain why <6" is bad and >6" is OK, apart from some dubious reg says so?

 

[richy3333]

To add, there's no requirement to fit a 100mA time delayed RCD, but circuits need to be protected by 30mA RCD/RCBO. Gas meter minimum of 150mm and 25mm away from electrical cables.
Work is Part Peeee notifiable if you are in Ongaland or Welsh Wales

 

[telectrix]

beats me. a gas leak and an arcing termination don't measurew the distance before blowing the house to bits.

 

[Silly Sausage]

beats me. a gas leak and an arcing termination don't measurew the distance before blowing the house to bits.

Just mental, meters and stuff are usually in a cupboard as well!
I've got an all time favourite (verging on madness) from the CORGI regs, I'll scan and post it if I can find them.

 

[Tuttle]

What's with the time switch, I couldn't work that bit out? It seems to be connected directly to the cut-out via some very small tails and it looks like there is also red wire between the time switch and the meter, but this isn't very clear on the photo so perhaps I am mistaken. I guess it's probably redundant now but I'd be interested to know what it did/does and why it is connected in this way.

edit: Now I think about it I guess that it could be economy 7?

 

[Phaze-3]

Hi Phaze 3,

What was your Ze reading? You may need to add another, longer rod. As for the were to put it, only you will know what the condition of the ground is were you are.

You will need an up front 100mA time delayed rcd, then your cu with 2 x 30mA rcd or even better, fit all rcbo's.

I havent got my onsite guide with me but of top of my head, the db needs to be about 150mm from other services.

Jay



Damn it tel, do you not go to work????lol

The reading was something like 36Ohms. pretty high i thought

 

[Phaze-3]

What's with the time switch, I couldn't work that bit out? It seems to be connected directly to the cut-out via some very small tails and it looks like there is also red wire between the time switch and the meter, but this isn't very clear on the photo so perhaps I am mistaken. I guess it's probably redundant now but I'd be interested to know what it did/does and why it is connected in this way.

edit: Now I think about it I guess that it could be economy 7?

That was another question i ment to ask earlier as well but forgot. I have no idea why there is a time clock. Economy 7 does spring into mind but i can't see why they would have it at this property.

Anybody got any ideas??????

 

[Phaze-3]

To add, there's no requirement to fit a 100mA time delayed RCD, but circuits need to be protected by 30mA RCD/RCBO. Gas meter minimum of 150mm and 25mm away from electrical cables.
Work is Part Peeee notifiable if you are in Ongaland or Welsh Wales

Very surprised it doesn't need the 100mA RCD. Thats good to know.

Thanks Richy

 

[Phaze-3]

How close is the existing earth rod to the house? Under the eaves tends to result in dry ground and poor contact. I find a house for half an hour or so can help.

Not to sure where the existing one is. There is no evidence of where it is. The Earth just disappears into the ground.

 

[Octopus]

Not to sure where the existing one is. There is no evidence of where it is. The Earth just disappears into the ground.

And your view on Part P compliance with building regs is???????

 

[Engineer54]

First off install a new TT system, the existing one is a dead duck!! lol!! You need a minimum of 2 X 5/8'' extendable rods coupled together to give you the depth required to make the system a stable one, and with an added bonus of substantially lowering your Ra value. Locate the rod position at least 1m away (more is better) from any external house walls to miss original builders rubble etc. Oh, and use a flush to ground earth pit over the rod to protect the connection, and to facilitate future testing, as well as a visual means of identification of earthing location!!

Secondly, i wouldn't take any notice at all of richy3333 suggestion of NOT incorporating an S type 100 mA upfront RCD (which could be used in place of CU main isolator). This is a TT system, and totally relying on a single RCD for earth fault protection is not very sensible, The upfront S type RCD will be if you like, the Additional protection, that a normal RCD gives to a TN installation!! As for the type of CU you install that's up to you dual RCD, or the far better but costlier all RCBO...

 

[streetlighter]

Am i seeing it right in the photo, There appears to be 3x Wylex plug-in MCBs bodged in place of porcelain fuse carriers in that old MEM unit ? So the cover is left of all the time exposing Live parts ?

 

[richy3333]

First off install a new TT system, the existing one is a dead duck!! lol!! You need a minimum of 2 X 5/8'' extendable rods coupled together to give you the depth required to make the system a stable one, and with an added bonus of substantially lowering your Ra value. Locate the rod position at least 1m away (more is better) from any external house walls to miss original builders rubble etc. Oh, and use a flush to ground earth pit over the rod to protect the connection, and to facilitate future testing, as well as a visual means of identification of earthing location!!

Secondly, i wouldn't take any notice at all of richy3333 suggestion of NOT incorporating an S type 100 mA upfront RCD (which could be used in place of CU main isolator). This is a TT system, and totally relying on a single RCD for earth fault protection is not very sensible, The upfront S type RCD will be if you like, the Additional protection, that a normal RCD gives to a TN installation!! As for the type of CU you install that's up to you dual RCD, or the far better but costlier all RCBO...

I don't necessarily disagree about the 100mA RCD, but perhaps you could quote the REg that requires it? Just re-read my previous post I didn't say to NOT incorporate a time delayed 100mA RCD, but highlighted it is NOT a requirement of BS7671, unless of course you can advise differently?