British gas TT earthing and rcds

[D Skelton]

WP, you're just lazy!

Everybody knows that 10 ohms is better than 200 ohms. Of course, there will be absolutely no difference whatsoever in how the system operates, but 10 is lower than 200, so it must be better?!

;-)

 

[Engineer54]

Someone else that sounds over bored!! lol!!:juggle2:

 

[Nightmare1308]

No, you just thought you'd try being a clever dick again!! lol!!

I stated that most of these metermen know less than a electrical trainee. But i can just guess as to what the earth rod installation is like and the sort of Ra value that has been obtained!!

Now if this district heating project has such a high monetary value, there shouldn't be any financial restrictions to actually providing a sub 1 ohm TT system, but will it ever get such a TT installation?? Very doubtful in the UK, after all there is always an RCD to bung in!!

how can you obtain a steady sub 1 ohm reading which you can guarantee not to fluctuate due to weather drying up ? will the circuit meet its 0.2s or 1s disconnection times depending on circuit design?
just a question...

 

[D Skelton]

how can you obtain a steady sub 1 ohm reading which you can guarantee not to fluctuate due to weather drying up ? will the circuit meet its 0.2s or 1s disconnection times depending on circuit design?
just a question...

In certain areas, subject to ground conditions, it can be done, and very easily. I have done it, as will have any electrician worth his salt. It won't ever have been on a domestic though that's for sure. Last time I did it was at the intake building for a large agricultural installation.

Ten or so underground sub mains fed from the intake position. It was either a decent earthing system or £2k for an up front s-type for the whole complex, which in itself would have been idiotic.

 

[netblindpaul]

TT does not equal hit a single 3/8" dia 4' rod in the ground, just in case some don't realise that.

 

[D Skelton]

TT does not equal hit a single 3/8" dia 4' rod in the ground, just in case some don't realise that.

I think that's a gross overestimation of most current day electricians knowledge of TT systems Paul. 3/8" twigs are the only language they speak nowadays.

 

[davesparks]

how can you obtain a steady sub 1 ohm reading which you can guarantee not to fluctuate due to weather drying up ? will the circuit meet its 0.2s or 1s disconnection times depending on circuit design?
just a question...

Start with 2x 5/8"x8' rods spaced 10' apart and then test it and take it from there.

 

[Nightmare1308]

In certain areas, subject to ground conditions, it can be done, and very easily. I have done it, as will have any electrician worth his salt. It won't ever have been on a domestic though that's for sure. Last time I did it was at the intake building for a large agricultural installation.

Ten or so underground sub mains fed from the intake position. It was either a decent earthing system or £2k for an up front s-type for the whole complex, which in itself would have been idiotic.

Nice
how do you no you could achive this, or did you try first then go from there or was there some sort of calculations/ science behind it ? just curious as you said before most electricians would just get the RCD out ? Even when I've spoke to the NICEIC they said Rcd done?..

 

[netblindpaul]

Damien,
I got bombed off one site on cost.
They then had to get a TT put in for a new location, the issue was they could not hit a rod in as 2m below the surface was an Ex area!
They ran a 50m cable down the site to a rod outside the Ex area, me, I'd probably have considered a horizontal electrode system, and got a lower value, I heard through the grapevine they struggled to get 200 Ohms, as it was made up ground.
The client even had their own earth moving equipment on site, hence why I would have considered a more local horizontal net/mat a metre down more reliable than a 50 m run to a 3/8" 4' vertical rod!

 

[netblindpaul]

Does anyone actually have a copy of BS 7430 that they refer to when undertaking their own earthing of electrical installations?

 

[trev]

I think that's a gross overestimation of most current day electricians knowledge of TT systems Paul. A single 3/8" twig is the only language they speak nowadays.

Sorted that for you Damian.

 

[JD6400]

Damian , how did you account for 705.411.1 if it was agricultural ?



Edit ; I have been on the sauce , so may be missing something :49:

 

[netblindpaul]

Start with 2x 5/8"x8' rods spaced 10' apart and then test it and take it from there.

They would be too close together then!

 

[D Skelton]

Damian , how did you account for 705.411.1 if it was agricultural ?



Edit ; I have been on the sauce , so may be missing something :49:

Neither the main panel or any of the sub mains it fed were in areas that could be deemed agricultural. There were sub mains elsewhere that fed areas where livestock was kept, therefore 705 would only apply in those areas.

 

[netblindpaul]

Neither the main panel or any of the sub mains it fed were in areas that could be deemed agricultural. There were sub mains elsewhere that fed areas where livestock was kept, therefore 705 would only apply in those areas.

Segregation a wonderful thing as long as it's not "Apartheid"!