EIC for submain db rewire

conrad · Mar 17, 2018

There is no other services ie water gas... in the building im part rewiring. They do however want another new DB to be fed from DB2 via another 32A mcb, to be located in a steel structure greenhouse for growing plants and veg so i assume may have sprinkler system. Anyone done anything in similar enviroment.

conrad · Mar 17, 2018

There is no other services ie water gas... in the building im part rewiring. They do however want another new DB to be fed from DB2 via another 32A mcb, to be located in a steel structure greenhouse for growing plants and veg so i assume may have sprinkler system. Anyone done anything in similar enviroment.

davesparks · Mar 17, 2018

Vortigern said:
Could you enlarge on that a bit please?

MCBs don’t fully discriminate with MCBs, and here the OP has a 63A mcb feeding a 32A mcb feeding a DB with (presumably) MCBs feeding final circuits.
There’s no way they’ll achieve discrimination with that setup.

Richard Burns · Mar 17, 2018

For your work you need to ensure the supply is suitable for the work you are doing and that the work you are doing is compliant, you also need to ensure that earthing and bonding is adequate for the protective measures you are using.
The 32A MCB you have stated at one point is supplying DB4 and you also seem to state it is supplying DB3.
If DB3 is supplied via a 32A type 2 MCB with Zdb of 0.70Ω and the cable incoming is suitable to carry 32A then this is compliant, except for the discrimination issues, which you cannot address.
You wish to add 4 sockets (circuits or individual sockets?), 2 spurs (presumably 13A?) and 4 lights (again circuits or individual lights).
If you are adding 4 individual sockets, 2 13A spurs and 4 individual lights then the supply could well be suitable for the load, depending on diversity since this is a shop it may have long term demand at full load.

The second DB to be installed in a greenhouse is more inconvenient, but you would need to ensure that the DB is protected against the external influences expected and bonding of the steel frame of the greenhouse may well be required, subject to appropriate assessment and testing. Therefore if that were the case then I would expect an additional bonding conductor would be needed.

conrad · Mar 17, 2018

Sorry for the confusion. My initial post refers to main DB as DB1... Regardless of names it is the third submain ie DB main, DB1, DB2 and DB3.

conrad · Mar 17, 2018

My question wasnt about the correct way to install etc im aware of all points people have mentioned... More on how far would people go ensuring everything inline was adequate simply to provide just a quote and what tests would you carry out as could be very time consuming in this circumstance. Also on what details you would input on EIC as some have said they would only check submain woring on and mains. As we know alot would install without a thought. Explainig to clients isnt simple either, especially if it creates more work as "its been like that for years"will be their reaction...but taking into account all the points being made on adequacy of current installation etc would you just refuse to do anything unless all points are met. Thanks for replies peeps. In terms of discrimination it is as follows. I shouldve been more clear with details at start apologies...
Cutout
3phase 100A bs1361 feeds
DBmain (8 way)
3P MCB 60Amp 16mm4c (swa cpc) feeds
DB1 - 3Phase (8 way)
3P MCB 63A dont know cable size feeds
DB2 which has a 100A RCCB 30mA main switch and is 3 phase.
32 A single phase mcb (attached image) 6mm 3 c swa feeds
DB 3 which has 100A RCCB 30mA main switch single phase 5 way DB.. Think thats pretty accurate but is from memory as details are in the van which is outside and its cold .

Toneyz · Mar 17, 2018

conrad said:
My question wasnt about the correct way to install etc im aware of all points people have mentioned... More on how far would people go ensuring everything inline was adequate simply to provide just a quote and what tests would you carry out as could be very time consuming in this circumstance. Also on what details you would input on EIC as some have said they would only check submain woring on and mains. As we know alot would install without a thought. Explainig to clients isnt simple either, especially if it creates more work as "its been like that for years"will be their reaction...but taking into account all the points being made on adequacy of current installation etc would you just refuse to do anything unless all points are met. Thanks for replies peeps. In terms of discrimination it is as follows. I shouldve been more clear with details at start apologies...
Cutout
3phase 100A bs1361 feeds
DBmain (8 way)
3P MCB 60Amp 16mm4c (swa cpc) feeds
DB1 - 3Phase (8 way)
3P MCB 63A dont know cable size feeds
DB2 which has a 100A RCCB 30mA main switch and is 3 phase.
32 A single phase mcb (attached image) 6mm 3 c swa feeds
DB 3 which has 100A RCCB 30mA main switch single phase 5 way DB.. Think thats pretty accurate but is from memory as details are in the van which is outside and its cold .

That is very poor discrimination between RCD's if something with a earth fault is plugged in on DB3 this could trip out DB2.

Richard Burns · Mar 17, 2018

So the situation changes again.
You have no discrimination between boards and you now have no discrimination between RCDs as well.
So a short circuit at DB3 could readily take out DB 2 as well.
An earth fault DB3 will also take out DB2.
However this is not what you are installing. Though you would need to check the RCD is working which will be a nightmare of overlap.
Since you are doing a rewire of a whole area, I would say that you should also attempt to find out the supply cable size between DB1 and DB2.
Then you will be able to enter the circuit description details of the submains on the EIC, Zdb only being relevant at DB3.
Full circuit details and tests would be needed for the circuits you are rewiring from DB3.

[ElectriciansForums.net] EIC for submain db rewire

conrad · Mar 17, 2018

anthonybragg said:
That is very poor discrimination between RCD's if something with a earth fault is plugged in on DB3 this could trip out DB2.

Client says it occasionally trips at DB2 but it only feeds a couple of sockets and a light within the outbuilding the db is located in( which isnt occupied) and a greenhouse db so isnt a major inconvenience..

conrad · Mar 17, 2018

Richard Burns said:
So the situation changes again.
You have no discrimination between boards and you now have no discrimination between RCDs as well.
So a short circuit at DB3 could readily take out DB 2 as well.
An earth fault DB3 will also take out DB2.
However this is not what you are installing. Though you would need to check the RCD is working which will be a nightmare of overlap.
Since you are doing a rewire of a whole area, I would say that you should also attempt to find out the supply cable size between DB1 and DB2.
Then you will be able to enter the circuit description details of the submains on the EIC, Zdb only being relevant at DB3.
Full circuit details and tests would be needed for the circuits you are rewiring from DB3.
View attachment 41417

Also the 63A @ db1 after the 60@ dbmain

conrad · Mar 17, 2018

Into DBmain from metering. Poor installation all round really. Main earth looks to be 10mm to met then 25mm into dbmain. Cant see incomer as 2 obsolete cables are cut sticking out covering it.

davesparks · Mar 17, 2018

That looks a lot like one of the tails entering through a separate hole in the steel enclosure, so you’ve got another non-compliance.

Toneyz · Mar 17, 2018

davesparks said:
That looks a lot like one of the tails entering through a separate hole in the steel enclosure, so you’ve got another non-compliance.

That's it Dave kick him when he's down, these non-compliances are acuminating.And there is abrasive edge (no bush/Gromit to cable entry on left.

conrad · Mar 17, 2018

Observed, thats why i took the pic. Its Neutral and Earth. Also no lid for the trunking header which creates an Ip4x issue in top of db. I think these old brown tails are single insulated? Again where would you go with these. Observations on existing installation could be alot of work alone. These would hopefully have all been highlighted in the latest eicr.

Toneyz · Mar 18, 2018

Comments on existing installation.

EIC for submain db rewire

conrad

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conrad

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davesparks

Richard Burns

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conrad

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conrad

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Toneyz

Richard Burns

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conrad

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conrad

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conrad

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davesparks

Toneyz

conrad

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Toneyz

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