Discuss EIC for submain db rewire in the Commercial Electrical Advice area at ElectriciansForums.net

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conrad

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Part Rewire to do, small shop on a large premesis 4 lights, 2 sockets, 2 spurs...The existing DB(DB4) which is staying, is fed via 32A mcb from a sub main DB3. Fed by 63 A mcb in another DB2 which then goes to DB1 which is connected to origin. Took a while to chase through as all DBs are in seperate buildings. My question is how far would you go on the EIC in terms of inspect and test details of each protective devices and cable sizing in line etc as job will more difficult obviously access and isolating testibg at each point in 4 seprate buildings.
 
One schedule of inspections and test results stating which DB the DB you're working on is fed from with Zdb etc.
 
The EIC for the rewire of the submain needs to cover "both ends" of said submain.

Whats the zbd at the last CU?
 
3 phs Cutout. All brown singles 35mm ish main earth looks 10mm appears to be undersized for installation. Ze 0 24
MainDB at cutout in main building feeds
DB1 seperate building 40 meters away
feeds
DB2 in an external outbuilding
Feeds
DB3 another outbuilding. Zdb 0.70 TNCS.
 
So DB4 which you are installing new circuits to is fed from DB3 via 32A MCB. What is the Zdb at this DB?as max Zs for a C 32 MCB is 0.68! and that's the 100% figure.
 
Sounds like submains fed from submains which is a discrimination nightmare
 
What type of Crabtree mcb is it. I agree discrimination is to pot but sometimes you can only work with what you have. If main protective bonding is required at your premises is the cpc of the supply cable to DB4 of a suitable csa to support bonding. I would check the supply cable from DB3 to 4 is adequately sized and whether fault protection is maintained by the supply protective device at DB3.
 
But i havnt checked cable sizes at each point in line to DB3. Again being in different buildings its alot of work to actually do, before doing the job you are being paid to do. Eg if the db1 or db2 had an underated cable or any other issues then connecting anything after these wouldnt be acceptable.
 
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.
 
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.
 
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.
 

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