Modifying Industrial Board

[Dunx]

Hi,

I would appreciate some thoughts on this! Site has a 42 way industrial board fed by 3 core 10mm wire armoured sub main. Ze at the board was 0.60ohms, the sub main must be 60 mts long as it is fed from the mains position in a neighbouring building.

The DB has an earth electrode and bonding to both gas and structural steel work, I didn't disconnect these when testing for ZE for access and practical readings! The DB [Hager] has a 100A 30ma main switch controlling everything in the workshop. Clerly when there is a fault everything goes out, not a great scenario.

What I proposed to do was to change the main 30ma for a 300ma time deayed one and then change the MCB's for RCBO's to protect the circuits that need them. I think that seems a reasonable solution that meets the regs but the difficulty is is that there are 3 phase mcb's, about 6 from memory and most of them are to sockets, so will need 30 ma protection. Hager don't do 3 phase RCBO's and for a whole range of reasons i don't want to rewire all this lot to a separate board. Does anyone have any ideae what I could use in the board for 3 P RCBO's...?!

Cheers

 

[steptoe]

is it TT earth?

or TN ?

 

[Dunx]

Hi,

Its both......There is an earth elecrode outside connected to the DB in question. The DB sub main is fed from TN at source, can't remember whether it was via wire armouring or core. Whats the issue there please?

 

[steptoe]

whats the TN?

TN-S or TN-C-S?

if its TN-C-S then you need to find out if its PME,

it may simply be a localised PME,

but, it deffo cant be TN and TT  :|

either way, the Ze/Zdb is too high for it to be PME as it stands, you need to get it tested on its own, and find why/where the high reading is from, or else, if it is suitable to do so, change it to a standalone TT.

 

[wozz]

3 core feeding a 3 phase board?

 

[Dunx]

Its TNS where it enters the mains/meter position. From there a sub main feeds the DB I am talking about via a wire armoured cable. The Workshop DB is therefore connected to the TNS and also connected to an earth electrode. I don't know why the spark used both!

3 core feeding a 3 phase board?

And neutral

 

[steptoe]

right, you need to decide on which system you want to use and disconnect the other system,

you cannot mix earthing systems within the installation on the same DB.

 

[SLIPSHOD & SLAPDASH]

3 core feeding a 3 phase board?

Also a  14 way, 3 phase   (42 ways) board fed by a 10mm cable  with at least a 60m run seems a bit small to me.

If you do/it is a TT then the main Rcd should be outside the metal enclosure ( certain applications it may not) 

Its TNS where it enters the mains/meter position. From there a sub main feeds the DB I am talking about via a wire armoured cable. The Workshop DB is therefore connected to the TNS and also connected to an earth electrode. I don't know why the spark used both!

And neutral

The  installer may have not connected the armouring at the gland ?

 

[steptoe]

Also a  14 way, 3 phase   (42 ways) board fed by a 10mm cable  with at least a 60m run seems a bit small to me.

If you do/it is a TT then the main Rcd should be outside the metal enclosure ( certain applications it may not) 

I have a 10mm to my shed and was concerned it was too small! <20m

Hi,

I would appreciate some thoughts on this! Site has a 42 way industrial board fed by 3 core 10mm wire armoured sub main. Ze at the board was 0.60ohms, the sub main must be 60 mts long as it is fed from the mains position in a neighbouring building.

The DB has an earth electrode and bonding to both gas and structural steel work, I didn't disconnect these when testing for ZE for access and practical readings! The DB [Hager] has a 100A 30ma main switch controlling everything in the workshop. Clerly when there is a fault everything goes out, not a great scenario.

What I proposed to do was to change the main 30ma for a 300ma time deayed one and then change the MCB's for RCBO's to protect the circuits that need them. I think that seems a reasonable solution that meets the regs but the difficulty is is that there are 3 phase mcb's, about 6 from memory and most of them are to sockets, so will need 30 ma protection. Hager don't do 3 phase RCBO's and for a whole range of reasons i don't want to rewire all this lot to a separate board. Does anyone have any ideae what I could use in the board for 3 P RCBO's...?!

Cheers

why would the 3p sockets require 30mA protection?

Dunx, not trying to be clever here,

but do you have any knowledge or experience on this sort of stuff?

seems you are asking a lot of fairly basic-ish questions TBH.  :|

 

[Dunx]

Ok so lets say we use as a TT system......!

 

[Evans Electric]

You won't need RCBOs for the 3ph final circuits will you ? 

RCBOs for any 13A skyrockets .

If its TN-S  then leave it as such.

 

[Dunx]

I have a 10mm to my shed and was concerned it was too small! <20m

why would the 3p sockets require 30mA protection?

Dunx, not trying to be clever here,

but do you have any knowledge or experience on this sort of stuff?

seems you are asking a lot of fairly basic-ish questions TBH.  :|

They use some 3 phase equipment outside.......and no I don't have a great deal of experience on industrial kit!

 

[Evans Electric]

How much do they use outside ?    Could you fit a Commando style IP65 socket c/w RCD   ( about £100 ea though)

 

[Sidewinder]

You can add a supplementary rod to a TN system with suitable precautions.

Be very careful of putting RCD's on Comm/Ind.

 

[steptoe]

You can add a supplementary rod to a TN system with suitable precautions.

Be very careful of putting RCD's on Comm/Ind.

stuff like that gets even more involved than even just simply adding extra rods to PME though sidewinder,

thats why I said a choice needed to be made,

OP has said he doesnt have a load of experience with this type of stuff,

Im not even very keen on rodding TNS in most circumstances.

 

[ProDave]

THREE core submain to 3 phase board.

So there are NO single phase loads at all from that board then?

 

[SLIPSHOD & SLAPDASH]

THREE core submain to 3 phase board.

So there are NO single phase loads at all from that board then?

Post #6 he does say and neutral.

 

[kme]

My initial concern is going to centre on the OCPD of that submain - 0.6 ZsDB????? Doesn`t leave much in the supply - though having an RCD incomer to a 42 way board is enough to concern me, ignoring everything else.

Then add the fact that this DB has a 60 metre run of 10mm.........Off the top of my head, you`re not going to be able to put much bigger than a 50A 60898 up front - or have I missed summat?

O/P - without fairly extensive knowledge of this type of installation, you`ll struggle with the design element. If you can have a qualified person do a design (suitably verified), and you want to follow a spec (i.e. construction side of the install) - that would be understandable; but, even with our collective - from afar - I can`t envisage a positive outcome to your re-design of the installation, to be honest.

Are you aware of exactly how many sets of regulations might apply? There`s more than you`d think - and you need sight of, or a good working knowledge of most of them, in order to provide a suitable design for, what sounds to be, a bit of an odd install.

No offence intended.

 

[Dunx]

Morning all,

Thanks very much for the advice! I am going to write to the workshop owner and suggest that he gets a formal design done by a suitably qualified engineer. I have heard more than enough to concern me and I don't want to be responsible for getting it even slightly wrong!

Cheers

Dunx

 

[kme]

Think its the safest option, to be honest