New dist. board

[Hawk]

Have a job coming up to supply a new distribution board. I am planning on running a 25mm 4 core swa and 16mm earth of a distance of 30mtrs from incoming supply to new board. The supply is 3 phase 100a tncs. I was thinking of coming out of the Henley blocks into a 100A Glasgow switched fuse and then the swa out of the switched fuse to a 80A 30mA 4pole rccb supplying the new board. Thoughts?

 

[Andy78]

Why an extra earth cable ?
Why an RCD and where exactly would it be positioned ?

Would be my immediate thoughts.

 

[Hawk]

I find it good practice to run a separate earth instead of using the swa. The rcd would be positioned below the board then tails out of it into the main switch. Reason for rcd is because it is a production area with access to outside where outdoor equipment may be used.

 

[Andy78]

I find it good practice to run a separate earth instead of using the swa. The rcd would be positioned below the board then tails out of it into the main switch. Reason for rcd is because it is a production area with access to outside where outdoor equipment may be used.

An extra earth is completely unnecesary, but whatever that's your choice.

One RCD covering the whole DB ? What size is the proposed DB and how many circuits and of what nature and use are the final circuits ? Do you think this will comply with the regs ?

 

[Pete999]

If the customer can stand the price install a 5 core SWA

 

[joehat]

Why 4 cores? Why not 2core?

 

[Pete999]

Why 4 cores? Why not 2core?

Three Phase supply

 

[Welchyboy1]

my standard set up would be, tails to switchfuse unit, swa to distribution board with main switch then rcbos for circuits that require it, or even better if containment allows, rcd socket outlets and no rcd potection at db at all

swa as cpc

if its to supply machines used in production, the last thing you need is that rcd mainswitch knocking out the whole area every time you get a small problem on one circuit

and why would you have it as a stand alone unit rather than as part of the db?

 

[Hawk]

I know what your saying, but as usual it's all down to cost. A 32A TP socket with rcd is around £360.

 

[Welchyboy1]

I know what your saying, but as usual it's all down to cost. A 32A TP socket with rcd is around £360.

Well if cost is the issue, then you need to give the customer the options(with the possible negaitive effects of cheaper choices)

and let him decide, and put it in his court when or if there are any issues later on

you dont want the phone calls in a months time that the machines are abit leaky and keep knocking out the whole board!

if you give him the choice at the start, problems afterwards are billable!

 

[Andy78]

I know what your saying, but as usual it's all down to cost. A 32A TP socket with rcd is around £360.

No it's not all down to cost it's about appropriate design and compliance with the regs.
Is that what price you have been quoted for a 32A RCD socket ? because if you look around they should easily be less than a hundred each.
RCBO is not an expensive solution is it ?

 

[Hawk]

True. I will give them the options and they can decide.

 

[Andy78]

True. I will give them the options and they can decide.

I'd give them the option of you designing the installation appropriately, safely, and compliantly, or you walking away.

 

[Hawk]

For some people it is about the price. How would what I described not be compliant with the regs?

 

[Andy78]

For some people it is about the price. How would what I described not be compliant with the regs?

Take a look at 314

 

[Hawk]

Haven't the regs to hand but I'm guessing minimum disruption?

 

[Hawk]

http://www.neweysonline.co.uk/mk-electric-single-socket-outlet-prewired-30ma-rcd-protected-tp%2Bn%2Be-32a-380-415v/1050079403/ProductInformation.raction

 

[Andy78]

Haven't the regs to hand but I'm guessing minimum disruption?

I think if you are designing a commercial production area installation and you are not aware of the requirements you are going to need your regs at hand.
Also if you are pricing a job using random internet prices instead of getting accurate quotes from wholesalers you're going to price yourself out of the job anyway.

 

[Hawk]

The job isn't for a while yet so haven't sat down and designed it yet. Was just getting opinions and suggestions. 2 heads is better than 1 and all that! I only use the internet for rough ideas on prices. I will get a quote from wholesalers once I have it designed. It will be inline with the regs as is all my work, so yes will have it at hand once I get the time to sit down and plan it out.

 

[Flanders]

First thing is check if rcd protection is actualy required there are ways of designing the installation so that rcds are not required , im not saying you won't need rcds but look at alternatives first

 

[Leesparkykent]

I know what your saying, but as usual it's all down to cost. A 32A TP socket with rcd is around £360.

Is the 32A TP socket for a specific piece of equipment?

 

[Darkwood]

Cost can be argued against lost production, if you have a fault you have lost the whole production area with your design, yes these outlets are costly but to comply to regulation regarding disruption then you have to explain this to the customer, having done commercial and industrial most of my career, I would never fit a 30mA front end on a distribution board unless special circumstances exist and/or it was otherwise requested by a designer of the install if that wasn't you - even then I would be holding a meeting to express my concerns.

The extra's to have RCD protection at the point of load where upfront protection isn't needed for cables etc may be thousands of pounds but to lose half a day or more production while an electrician comes to clear a fault they cannot isolate would probably dwarf the cost of designing it correctly in the first place, if this is about saving a few quid then you need to have a sit down and talk with the customer.

 

[shanky887614]

i wouldnt bother with an rcd but thats not to say i might not have a safety circuit that can shut large amounts of the installation out.

most industrial installs dont need an rcd.

why do you need an rcd? most machines have multiple guards/barriers to keep the operators away from the cables etc.

a company would rather pay £2000 than 200 if it means they wont be getting nuisance tripping causing a high loss of production

 

[Hawk]

Was thinking rcds as its a production area and you know what cleaners are like with hoses!

 

[shanky887614]

Was thinking rcds as its a production area and you know what cleaners are like with hoses!

do you design many of these types of installations?

usually the shop power is commando sockets and dedicated cleaning sockets where needed

 

[Hawk]

I mean when the cleaners are in they hose down everything

 

[shanky887614]

I mean when the cleaners are in they hose down everything

then your install doesnt comply with regs and isnt suitable for the enviroment and you need an ip rated install

rcd's are not designed to constantly trip

 

[Hawk]

All the isolaters and sockets will be ip rated

 

[Flanders]

As shanky says fit suitable equipment for the environment not rcds ,

 

[Hawk]

Nothing is confirmed yet I only met the client the other day so still a few meetings etc. before anything is finalised.

 

[Flanders]

All the isolaters and sockets will be ip rated

Then what is the rson for rcds is it portable equipment that is being used outside ?

 

[Hawk]

The machinery is stainless steel, so was more thinking if water got into any of the connections.

 

[Flanders]

The companys method statement should say somthing in the Lines of Isolate the equipment before cleaning , do not use high presure water on equipment etc.

 

[davesparks]

Have a job coming up to supply a new distribution board. I am planning on running a 25mm 4 core swa and 16mm earth of a distance of 30mtrs from incoming supply to new board. The supply is 3 phase 100a tncs. I was thinking of coming out of the Henley blocks into a 100A Glasgow switched fuse and then the swa out of the switched fuse to a 80A 30mA 4pole rccb supplying the new board. Thoughts?

16mm separate earth is most likely oversized and a complete waste of time and money to boot, if main bonding is required at the sub-board then a 10mm bond will be required, but not if no main bonding is to be connected there.
Glasgows are fused switches not switched fuses, there is a difference.
An 80A RCD is no good on a 100A supply.
A 30mA RCD covering a whole board is just plain ridiculous.

 

[davesparks]

I mean when the cleaners are in they hose down everything

So make sure the install meets the appropriate IP rating, or is put into suitable enclosures. An RCD won't stop anything from getting wet, it will just switch it off and water will continue to enter the equipment.

 

[Hawk]

I think the best option is use individual rcds if required. So instead of the 16mm earth would you just use the swa?

 

[Darkwood]

I think the best option is use individual rcds if required. So instead of the 16mm earth would you just use the swa?

Using a seperate earth for the size you suggested wouldn't normally be required although it may be necessary in certain circumstances like reducing Zs due to high upstream initial values or bonding requirements may warrant running a seperate earth.

 

[davesparks]

I think the best option is use individual rcds if required. So instead of the 16mm earth would you just use the swa?

Yes, following on from carrying out the calculations I would use the armour. If the armour is not sufficient then I'd look at using a bigger cable or a fifth core within the cable.

 

[Hawk]

Had a look at the current set up. There is a main DB and 2 sub DB's. 1 of the sub boards is supplied from a fused switch and the other one is supplied from a 63A TP MCB. I would have thought both sub boards would have been supplied by fused switches.