Using Type D MCB for discrimination

[Michaelwgroves]

I've just been on phone with Hager designing domestic distribution board design. Engineer advised using Type D 63A in distribution board supplying CU to give better discrimination. Looking at tables anything over 10A on CU might also trip Type D, but it does give a better chance.
So I need to make sure this is okay, I've found reference to 16th edition Regulation 413-02-08. But this has been moved in 17th edition and I can't find anything. Has anyone got any pointers and thoughts about using Type D breakers for domestic distribution panel?

 

[westward10]

Have you checked out the maximum Zs on a D, 63A.

 

[DPG]

Wouldn't a fuse be better? You would get your discrimination then.

 

[Ian1981]

Well using a type D mcb @ 63 amp would give a maximum zs of 0.35 ohms for a maximum disconnection time of 5 seconds being a distribution circuit, that’s without the 0.8 correction factor
Typically it’s very difficult to achieve your zs values using type D for lower rated mcbs using 0.4 seconds as their maximum disconnection times as the typical zs values are Uo x cmin/ In x 20

I would suggest using a bs 88 fuse for protection of your submain tho.

 

[Octopus]

Its an interesting thread this ...................... there are so many submains in service supplied from standard type B MCB's .............. including one in my shed.

But if this is protection from the DNO fuse to the CU what do you do if the DNO fuse is 60A

 

[Ian1981]

 

[Strima]

Its an interesting thread this ...................... there are so many submains in service supplied from standard type B MCB's .............. including one in my shed.

But if this is protection from the DNO fuse to the CU what do you do if the DNO fuse is 60A

One of our customers has some telecoms modules with no discrimination. Had a 16 amp C type trip out and it also took out the distribution circuit in the generator room and the main incoming 160 amp MCCB.

Luckily the DNO 200 amp fuses never broke a sweat...

 

[Leesparkykent]

You are only going to achieve partial discrimination at the very best. It's just carp design from the onset. Multiple 60898's in series for a supply to a shed isn't really going to be a drama if it trips and takes out the upfront Circuit breaker. Put the same situation in a factory where taking out the upfront circuit breaker could lead to loss of production and consequently loss of thousands of pounds...then you have a real problem. Also worth considering that due to lack of discrimination you may not be able to minimise disruption in the event of a fault.

 

[buzzlightyear]

Engineer advised using Type D 63A in distribution board supplying CU to give better discrimination

best with bs88 60amp has Ian Gallagher 1981 says.

 

[buzzlightyear]

MW, is this for Buckingham palace you working on in 5 years time
time lord!

 

[Leesparkykent]

Its an interesting thread this ...................... there are so many submains in service supplied from standard type B MCB's .............. including one in my shed.

But if this is protection from the DNO fuse to the CU what do you do if the DNO fuse is 60A

pick a 100A one up from the wholesalers and put it in place of the 60A one...play dumb if the DNO ask anything

 

[buzzlightyear]

pick a 100A one up from the wholesalers and put it in place of the 60A one...play dumb if the DNO ask anything

and rollover on the floor like a dog .

 

[Michaelwgroves]

Wouldn't a fuse be better? You would get your discrimination then.

Distribution board start to get big an expensive with fuses, unless you can recommend something smaller and more cost effective?

 

[Michaelwgroves]

Well using a type D mcb @ 63 amp would give a maximum zs of 0.35 ohms for a maximum disconnection time of 5 seconds being a distribution circuit, that’s without the 0.8 correction factor
Typically it’s very difficult to achieve your zs values using type D for lower rated mcbs using 0.4 seconds as their maximum disconnection times as the typical zs values are Uo x cmin/ In x 20

I would suggest using a bs 88 fuse for protection of your submain tho.

That's the answer I was looking for...... well actually not what I wanted but that kills this option dead. Looking at old EIC Zs up to 0.9, typically around 0.6

 

[DPG]

Distribution board start to get big an expensive with fuses, unless you can recommend something smaller and more cost effective?

Fuse holder module??

 

[Michaelwgroves]

But if this is protection from the DNO fuse to the CU what do you do if the DNO fuse is 60A

DNO fuse 100A

 

[buzzlightyear]

DNO fuse 100A

or 6in nail !

 

[Rocboni]

Fuse holder module??

You only get standard size fuseholders up to 32A any bigger and its a double module, so the busbar won't fit.

What not individual switch fuses?

 

[Michaelwgroves]

Fuse holder module??

Interesting, got any links I can look at?

 

[buzzlightyear]

What not individual switch fuses?

did tell him pike !

 

[Michaelwgroves]

You only get standard size fuseholders up to 32A any bigger and its a wider module, so the busbar won't fit.

What not individual switch fuses?

I'd need 5, Distribution panel seems like a better solution.

 

[buzzlightyear]

Ryefield Board | Ryefield Distribution Board | Sparks Direct - https://www.sparksdirect.co.uk/electrical-items/consumer-units/industrial-and-commercial/ryefield-boards

 

[Michaelwgroves]

Ian1981, thanks for attachments, not sure how to read. Say I have 63A Type D upstream and 20A Type B downstream. I think I have my up's and downs the right way!
I use first page which gives me 0.84 kA, so what does this tell me?

 

[Rocboni]

I'd need 5, Distribution panel seems like a better solution.

Maybe get a 10 way board fit 5 bs88 carriers p, not sure what you'd do about the busbar, unless you snip off energy second way ,

I'd be going with switch fuses though with separate meters on each if needed.

 

[Michaelwgroves]

Ryefield Board | Ryefield Distribution Board | Sparks Direct - https://www.sparksdirect.co.uk/electrical-items/consumer-units/industrial-and-commercial/ryefield-boards

I agree achieves discrimination, but it's 5 times the cost and not amendment 3 compliant, so I'd need to buy a bigger metal box to put it in

 

[Michaelwgroves]

Technical Properties LS201 - http://www.hager.co.uk/product-catalogue/energy-distribution/protection-devices/fuse-carriers/hrc-fuse-carriers-bs88/ls201/47120.htm

This looks perfect but only goes up to 32A like Rocbino said preciously. If they did same thing with 60A it would be perfect

 

[Rocboni]

PMX22 - 1P | Charter Controls - https://charter-controls.com/products/fuses-fuse-holders/pmx22-1p/

Don't think a busbar will fit though and might be right with 5 10mm SWA into the top of the CU?

Personally for me 5 switch fuses, some steel trunking and a 6 way Henley block, Then your SWA to each room.

http://www.lamps2udirect.com/electrical-accessories/eterna-cb100dp-double-pole-100a-connector-block/70396 about £300 total

 

[Rocboni]

Are they 10mm or bigger?

 

[Leesparkykent]

I agree achieves discrimination, but it's 5 times the cost and not amendment 3 compliant, so I'd need to buy a bigger metal box to put it in

Look at Eaton Excel distribution fuse board.

Edit: link Exel distribution fuseboards – Eaton UK – Power Distribution - http://www.eaton.uk.com/EatonUK/ProductsSolutions/Electrical/ProductsServices/PowerDistributionMonitoring/LVS/IndustrialSwitchandFusegear/Exel-DistributionFuseboards/index.htm

 

[Michaelwgroves]

I don't like using Henley, it just looks like an after thought.

I've just got off phone from Hager technical. This project falls through the crack of domestic and commercial. His solution which I like is; cut-out into empty CU with 100A main switch, populate with Hager KRN190's which are simply a straight through 100A MCB, but without a breaker. You would wire straight from KRN190 to switched fuse which would then achieve discrimination.

Technical Properties KRN199 - http://www.hager.co.uk/product-catalogue/energy-distribution/enclosures/metal-enclosures/metal-enclosure-accessories/krn199/42687.htm

 

[Michaelwgroves]

Look at Eaton Excel distribution fuse board.

Edit: link Exel distribution fuseboards – Eaton UK – Power Distribution - http://www.eaton.uk.com/EatonUK/ProductsSolutions/Electrical/ProductsServices/PowerDistributionMonitoring/LVS/IndustrialSwitchandFusegear/Exel-DistributionFuseboards/index.htm

Again not amendment 3 compliant

 

[Michaelwgroves]

Are they 10mm or bigger?

Is what 10mm ?

 

[Leesparkykent]

Again not amendment 3 compliant

What do you mean not amendment 3 compliant? It's a metal enclosure, with metal door, metal hinges and metal catches....what else do you want? You just choose what catch/lock you want when you order it? Same with the Ryefield that Buzz linked to earlier.

 

[Rocboni]

Is what 10mm ?

The supplies.

Can't see the point of spending money on a DB with straight through links, the Henley block could be sat ontop of the steel trunking which is slotted to accept the enclosed tails would look tidy enough.

 

[Michaelwgroves]

The supplies.

Can't see the point of spending money on a DB with straight through links, the Henley block could be sat ontop of the steel trunking which is slotted to accept the enclosed tails would look tidy enough.

Supply is 25mm,

Agreed Henley would achieve exactly the same, I just think DB would look more like it was designed that way from outset. Henley just looks like an after thought.
But I agree getting 5 no. SWA into DB might be a struggle, I'll need to consider bigger board if I go this route.

 

[Leesparkykent]

Bus bar chamber and switch fuses...it's fit for purpose and designed for the job. Out of meter into a 100A switch disconnector, into bus bar chamber, length of trunking slotted sat on top with paxolin between, bush switch fuses on to trunking, link bus bar chamber and switch fuses with singles in the trunking, gland SWA's into the switch fuses...Job done.

 

[Michaelwgroves]

What do you mean not amendment 3 compliant? It's a metal enclosure, with metal door, metal hinges and metal catches....what else do you want? You just choose what catch/lock you want when you order it? Same with the Ryefield that Buzz linked to earlier.

Door needs to remain closed when not in use so needs to be top hung. A lock is not sufficient apparently! Had this conversation with Hager today.
Seems crazy to me, but they are the regs as I understand them.

 

[davesparks]

Again not amendment 3 compliant

How on earth can you say that’s not amendment 3 compliant? It’s a proper metal clad industrial fuseboard with a sealed, screwed shut door, they contain fires much better than the thin little ‘domestic’ boards!

 

[Leesparkykent]

Door needs to remain closed when not in use so needs to be top hung. A lock is not sufficient apparently! Had this conversation with Hager today.
Seems crazy to me, but they are the regs as I understand them.

Well you've understood wrong then. There is no regulation stating door must be top hung and whoever told you such is talking out their arse.

 

[Michaelwgroves]

Bus bar chamber and switch fuses...it's fit for purpose and designed for the job. Out of meter into a 100A switch disconnector, into bus bar chamber, length of trunking slotted sat on top with paxolin between, bush switch fuses on to trunking, link bus bar chamber and switch fuses with singles in the trunking, gland SWA's into te switch fuses...Job done.

Much better solution, I like it.

 

[Michaelwgroves]

Well you've understood wrong then. There is no regulation stating door must be top hung and whoever told you such is talking out their arse.

The door must be self closing, that's the important bit.

 

[davesparks]

Door needs to remain closed when not in use so needs to be top hung. A lock is not sufficient apparently! Had this conversation with Hager today.
Seems crazy to me, but they are the regs as I understand them.

Well it constantly in use as the electricity will always be flowing through it whilst the installation is live!
Show me where in the regulations it says it must be top hung? And if that’s the case then what about the ‘amd3 cu’s’ that don’t have a self closing lid??

If it’s that much of an issue to you then get a busbar and switchfuse setup, square d do a modular busbar chamber with space for 6 switchfuses which come with pre-manufactured connecting links.

 

[Ian1981]

The door must be self closing, that's the important bit.

You better tell Schneider that their eazy 9 consumer units don’t comply then.

 

[davesparks]

The door must be self closing, that's the important bit.

So mount the excel board sideways!

 

[Leesparkykent]

The door must be self closing, that's the important bit.

Explain this then? BG consumer unit.

 

[Rocboni]

Much better solution, I like it.

You said this was overkill on another thread. It is the best solution, and a "no brainer"

 

[Michaelwgroves]

I think the evidence is overwhelming, I agree what I was told today must be incorrect........

 

[Ian1981]

I think the evidence is overwhelming, I agree what I was told today must be incorrect........

Have a look on YouTube for hagers amendment 3 myth breakers regarding metal consumer units.
Whether the lid debate is on there , I can’t remember but worth a watch anyway.

 

[Octopus]

I think the evidence is overwhelming, I agree what I was told today must be incorrect........

But there will be muppets going around saying its the "law"

 

[Michaelwgroves]

You said this was overkill on another thread. It is the best solution, and a "no brainer"

I can't find that statement, but I have no problem doing a public U-turn when evidence proves my previous thoughts were wrong.