16 amp supply - Brightspark!

[rorie]

Evening all! I have a question or two about a 16 amp supply. I found a thread but didn't quite answer my questions.

I was going to PM Brightspark as he seems to know his stuff. How can i PM him? Or can anybody else help?

I have an old storage heater consumer unit (3 fuses) which now only feeds a supply (via 6mm T&E though just one of the fuses) to the garage where there is a modern CU with RCD protection.

1) I am going to add a 16amp type 'c' MCB in the garage CU (for a table saw). The CU manufacturer said its fine with the CU i have… but is there anything else i need to worry about or is it ok to pop that MCB in?

2) I am running a cable from the 16 amp MCB to the 16 amp socket (just the one socket). What is the advisable cable size? I believe 2.5mm is sufficient, but is it better to run a thicker cable if i have the option?

3) I want to replace the old CU in the house with a new one to get rid of the wire fuse. All i have seen so far is 'shower CU' which all have an RCD and a single breaker, or garage ones which have a couple MCBs. Would i be better putting in just a 'on/off' breaker (called a DP?) as i have an RCD down stream at the CU in the garage. P.s. i will not be doing this bit myself! I am getting a sparky down to just hook up and test, but want to be as prepared as possible to save on the pennies!

 

[brightspark]

its ok to put a 16amp mcb in the garage unit and 2,5mm cable to the 16 amp socket will be well adequate . what size fuse is in the 3 way unit back in the house

 

[rorie]

Your ears must have been burning Thanks for the reply!

So there is no real issue with he MCB being a 'type C'? I read that i need to do some special tests on the system for this….

Any thoughts about the old storage heating CU?

Cheers!

 

[Robotstar5]

So there is no real issue with he MCB being a 'type C'? I read that i need to do some special tests on the system for this….

Any thoughts about the old storage heating CU?

Technically you are supposed to check the higher curve mcb can achieve the correct disconnection times in the wiring regs, but no one seems to bother

Replace the old CU with the "shower CU"

 

[brightspark]

u can change the old unit in the house to a garage unit and providing the electricity board supply the main earth change the rcd mainswitch to a double pole mainswitch if u have rcd protection in garage .it was a tt system electricity board supply overhead 2 wire and no earth just a rod u would need rcd back at source

 

[Sidewinder]

Technically you are supposed to check the higher curve mcb can achieve the correct disconnection times in the wiring regs, but no one seems to bother

Replace the old CU with the "shower CU"

Yes they do!
Well I do because I have to fill in test certs and provide results, else I would be committing fraud.

 

[Robotstar5]

u can change the old unit in the house to a garage unit and providing the electricity board supply the main earth change the rcd mainswitch to a double pole mainswitch if u have rcd protection in garage...

That's interesting, as the garage is fed by T&E (OP hasn't stated what containment/protection) I would have an RCD at source?

 

[Robotstar5]

Yes they do!
Well I do because I have to fill in test certs and provide results, else I would be committing fraud.

You're right, but how many posts do you see on here about "just fit a C type mcb to stop welder tripping" without considering anything else?.

 

[rorie]

Thanks for the replies folks.

Here is a photo of the house set up. I have the main CU for the house and a second feed that goes to the old storage heating CU. They used to be split outside for a night time meter, but now are just two feeds from the one meter. The feed to the storage heater CU goes through a wire fuse and out with a 6mm T&E over to the garage where i have a Schneider Easy9 CU with a 63amp RCD, and various MCBs (the usual 32amp for sockets, 6amp for lights etc). It is here i want to add the new type C 16 amp MCB

and providing the electricity board supply the main earth

Sorry, now you have lost me! How do i know if they supply the main earth?

it was a tt system electricity board supply overhead 2 wire and no earth just a rod u would need rcd back at source

That's interesting, as the garage is fed by T&E (OP hasn't stated what containment/protection) I would have an RCD at source?

Again, a little lost! Perhaps the photo will help?

Alternatively, is it ok to replace this CU in the house with a 'garage CU' which has an RCD, AND keep my RCD on the CU in the garage? Or will having two RCDs cause any issues?

 

[Sidewinder]

Does it "need" an RCD in the house.
If not, then don't fit one.
If you do then if they are both instantaneous devices then there is no selectivity, so no telling which one will trip.
So you could end up always having to go back into the house to reset if an RCD trips.

 

[Sidewinder]

You're right, but how many posts do you see on here about "just fit a C type mcb to stop welder tripping" without considering anything else?.

I know Robotstar5, but just because that advice is given, does not mean it's correct.
You know that.

 

[brightspark]

to be honest if it was me id change the house unit to a 17 th edition 3d amendment metal cased unit and do away with the garage unit and fit an rcbo in it for the garage if the cable is burried in the wall or not mechanicaly protected. the thing is though how far do u go and what cost

 

[brightspark]

the only time id fit a c type breaker is on a dedecated circuit for high current start up machines. ring mains and general circuits a b type domestic use

 

[Robotstar5]

I know Robotstar5, but just because that advice is given, does not mean it's correct.
You know that.

I do, hence the smiley

 

[Sidewinder]

Ahh, now for some reason, no smiley on your post here! I hope this one works!

 

[rorie]

absolutely - the house CU needs changed. I am away to convert the upstairs (re-built most of the house!), at which stage the CU will be moved, and upgraded. This is just an interim measure:

I am having issues with my new table saw - the possible causes are a) the NVR switch b) The lack of 16amp supply (i was running off a 13 amp socket before) c) the lack of 'type c' mcb and d) the wire fuse in the house causing too many losses.

I have a new NVR, installed the 16 amp socket, direct line back to CU where the type C MCB will be installed, and now its just the wire fuse to solve!

I do not think i have any need for a RCB for this house CU. The current CU is a 'on/off' but needs routed through the fuse.

I am thinking replacing with one of these may be best, i.e. just a switch with no breaker in the house - the garage will provide all the protection. Does that sound acceptable?

http://www.toolstation.com/shop/Ele...er+Units/sd2615/Wylex+DP+Consumer+Unit/p12169

In regards to it saying its 'two way', does that mean it switches supply to two sources?

 

[Sidewinder]

What issues?
A rewirable fuse has negligible losses so that is a load of nonsense to start with.

 

[brightspark]

thats just a double pole mainswitch the 2 way means it will accept 2 minature circuit breakers.if u have a 6mm cable feeding your garrage fit a 32 amp mcb in that unit and it leaves one spare

 

[rorie]

Perhaps i should note, i am trying to resolve all the issues before trying the saw again - its not a case of the other possible causes have failed.

The saw is new, but has been struggling to start and not running on full power. Although it does not trip the circuits (hence i didn't think the CB had anything to do with it!), thought i would replace that anyway for the minimal cost.

The problems i am having is that when cold (first used and on a cold day) the saw starts fine. But as i use the saw, the NVR doesn't latch and i need to hold it 'on' until the motor is at full speed before letting go, otherwise it just dies.

 

[brightspark]

What issues?
A rewirable fuse has negligible losses so that is a load of nonsense to start with.

i think that 3 way old unit is only fitted with 16 amp rewirable fuses as it was only for nightstore heaters