300Ma 4 Pole Rcd - Pme Supply?

[Rob_the_rich]

I asked whether the 300mA rcd was an S-type because you will certainly have 30mA rcds downstream of it for your new extension. There wlll be no discrimination between these rcds, either could trip on a fault. 

So if the block containing the main intake becomes a stable, and the 300mA rcd trips, the whole installation goes off and the owner would have to go to the stable, past dobbin, to reset the rcd, possibly in the dark.

looking at the last sentence of 705.537.2 it looks like having the rcd, or any devices used for isolation, within a stable is a no-no too.

Sorry if my posts seem a bit condescending, tbh I have only looked at 705 once before iirc, wholly domestic for me.

Just want you to get it right, like everyone here does

As an aside, in lightning strikes, the wide spacing of livestock's feet means there is a larger potential difference  wrt the source of the strike, they are more "prone" to shocks than humans standing on two feet.

 

[jimmybobbob]

Been a while since I last spoke..... I'm embarrassed to say that the location was over looked (obviously just looking at the domestic extension) not meaning that I was compromising safety either as I've not actually carried out any work. The barns are being rebuilt and there is going to be a 100ma type s 4 pole rcd installed with a a nice new earth rod (and all steel work bonded) the theory i was getting at about which would trip first etc etc....If there was a fault of 1 amp, there is no discrimination...just the theory I was getting at such as you would expect a plug fuse to blow before any MCB (IN THEORY) obv depends on fault current

 

[steptoe]

how fast does an RCD need to trip to meet the regs?

how fast does an S type RCD have to trip to meet the regs ?

 

[jimmybobbob]

300/500...missing something again?

 

[steptoe]

I'll feed a bit on this one,

an S type, or TD [time delay] has a set delay at the beginning of the trip sequence, so its permissable trip time is greater than a 'normal' RCD

that is how you can gain discrimination,

not, as a lot of people mistakenly think, by using a larger rated device,

ie, 30mA 100mA 300mA  , should all trip within the same time allowance,

whereas an S type will have a larger timeframe to still comply.

 

[jimmybobbob]

Sorry please think of me arrogant or just thick...I'm missing tour point

 

[steptoe]

TBH

I cant think of any easier way to explain it,

my grasp of English isnt that good sometimes.

 

[jimmybobbob]

Are you telling me what I'm doing is wrong?

 

[jimmybobbob]

Not meant in a condisending way just from my OP....

 

[steptoe]

no, Im not,

because,

I have no idea what you now intend to do given all the various advice and guidance you have been given in this thread,

if, you are still going to go ahead with what you propose in the OP, then, given the limited information we have so far,

then,

I'd say it was wrong.

 

[jimmybobbob]

Ok...pvc enclosure in the meter enclosure housing the time delay rcd then tails out to the 3p DB (rightly or wrongly surely it's better the protect the tails as close as practicable to the install)

Earth rod with earth going to 3pDB

3 core swa supply to the house with dual 30ma rcd to do the dwelling fused via 63amp MCB,SWA obv bonded

30ma RCBO lights and power in new stables

Should I also note that the 3pDB is NOT actually in a stable as such that is in the store room with bikes tools etc (should of made that clear in my OP)

All steelwork in stable block bonded back to 3PDB

.....

DB is on the reverse side of the cut out so max run roughly 1.5 to 2 mtrs ish

 

[steptoe]

OK,

may be a good idea to read the relevant sections of the regs again,

doesnt matter where the DB is imho, but, the way I understand it, unless the supply originates from the 'farmhouse' , then no form of PME is permitted,

I understand as your supply being in a 'farm' building / stable, then I would say it should be TT,

BTW, you will more than likely need more than one rod, each location should preferably have its own rod, albeit interlinked, as you see fit.

you may also need interconnected bonding, only you can judge that on site.

personally, I'd also like to see a 4p isolator before the upfront RCD.

 

[jimmybobbob]

It is a PME supply,but the whole installation is going on an earth rod. The distance from the DB & Rod to the house is I'd say no more than 8mtrs... how is it different if it came from the house first?

There is a 4 pole service isolator straight of the meter