Fault protection - Busbar Chambers

[Lectrician]

We all know how it works...

800amp fuses protecting a busbar, and then 16, 25, 35 mm etc feeding 63amp, 100amp etc switch fuses bushed onto the busbar chamber.

Doing a periodic inspection I have come across a busbar which had limited space around it, so they have terminated SWA into the busbar chamber and run this for no more than 3m to a switch fuse, and then SWA out of the switch fuse.

I do not like this, and without double checking the regs, I think this is actually OK......

Thoughts?

On the same job there are actually a few SWA's terminated directly to the busbar chamber which feed TP boards across the site - no switch fuses installed. These are obviously non compliant.

 

[ricicle]

What size is this shorter SWA. Will the 800A fuses provide adequate fault current protection for it ?

Other than that if it is less than 3m it should be ok as the armouring reduces the risk of fault by damage and I take it there are no flammable materials nearby ?

As for the longer ones they don't comply with 433.2.2 (ii)

Obviously the SWA needs to glanded correctly also to be able to carry any fault current eg not into a removable lid held on by teeny weeny self tappers !!

 

[holmslaw]

..

 

[Adam_151]

Sorry to dig up an old thread, but did you reach a conclusion on this, Lec?

Just come across a similar situation myself, all be it on a slightly smaller scale and done the calcs and the sticking point seems to be fault protection to the armour in many cases

 

[kai]

It's a similar situation where a 500amp fuse in the substation, protects the ancient lead incomer in the hallway of your house (The incomer runs from floor level to the meter position 2metres up the wall) - No fault protection here for the supply cable in your hallway!

 

[Lectrician]

The conclusion was actually a new 800amp MEM MCCB board, an 800amp generator transfer switch, some 300mm galv trunk and some 240mm tri-rated singles (doubled up).

Oh, and a few days prep work followed by a full saturday shutdown....

I am still on site doing other works, so may take some pics.

 

[Lectrician]

It's a similar situation where a 500amp fuse in the substation, protects the ancient lead incomer in the hallway of your house (The incomer runs from floor level to the meter position 2metres up the wall) - No fault protection here for the supply cable in your hallway!

So, the same as all other homes then??

 

[Adam_151]

The conclusion was actually a new 800amp MEM MCCB board, an 800amp generator transfer switch, some 300mm galv trunk and some 240mm tri-rated singles (doubled up).

Nice...though does not look quite as impressive as a long line of switchfuses mounted along the top of a busbar ... busbars are a dying way of doing things these days due to the time taken arn't they?

The instance I came across was a 300A panelboard, somewhat obsolete and someone couldn't be bothered trying to source a MCCB for it, so they mounted a switchfuse to the side a bit, other side of the CT looped a bit of 35mm² 4c SWA with 16mm earth tied to side of it out of top of board, round the CT enclosure and into bottom of sw-f, lugged off the busbars in the panel ... I don't know why, because there was space the other side of the panelboard... could have put some strut up and mounted it to side of panel with a suitably sized couper and 35mm singles straight in....I suppose that would have been a bit more work ,and I'm not sure I like to see the panel used as a busbar chamber if its in anyway avoidable anyway!

Zs is on the limit for 5s disconnection on the 300A fuses, and the adaibatic just passes for fault protection of the 35mm cores... but fails for the 16mm earth and fails for the armouring

 

[ricicle]

Nice...though does not look quite as impressive as a long line of switchfuses mounted along the top of a busbar ... busbars are a dying way of doing things these days due to the time taken arn't they?

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• ricicle
• 19 Dec 2010
• 1

Untitled

• ricicle
• 19 Dec 2010
• 1

 

[tonyelectric]

Nice bits of kit Ricicle, MEM glasgow chambers if i'm not mistaken, nice orange paintjob on the second one (I still paint the conduits in school workshops orange!).
For me its the cast iron stuff from the era before sheet steel thats really impressive, always loved the ornate art deco decoration of Bill, Simplex, MEM, English Electric etc, for that matter ever seen the control room at Battersea

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• tonyelectric
• 19 Dec 2010
• 1

 

[Lectrician]

Not got any pics of the new kit yet - but here is what was pulled out.

 

[tonyelectric]

Dorman Smith eh. , don't see much of their stuff round these parts, replaced some of their sockets last week, I think they are a Manchester outfit so perhaps they sell more up north. Mostly MEM and Ottermill-Simplex round here although I encountered Mitsubishi boards and busbars in a school the other day, never knew they made DBs

 

[Adam_151]

Dorman Smith eh. , don't see much of their stuff round these parts, replaced some of their sockets last week, I think they are a Manchester outfit so perhaps they sell more up north. Mostly MEM and Ottermill-Simplex round here although I encountered Mitsubishi boards and busbars in a school the other day, never knew they made DBs

A lot of their older stuff says its made in Preston, so not a million miles from manchester

It seems to often be used quite extensivly on educational sites, due to being specified by the local authority.

Their new stuff is pretty good I think, the neutral block covers arn't great and the terminals on the RCBOs are a little naf, but other than that the boards themselves are pretty solid

Lec, thats the same site as you posted a pic of a while ago wasn't it, with the live ends of the busbars exposed due to badly fabricated trunking work?

 

[ban-all-sheds]

for that matter ever seen the control room at Battersea

I went on a tour of the place after it had been decommissioned but before they decided that the best thing ever would be to remove the roof and then leave it for several years.

 

[ricicle]

Hope you salvaged the copper busbars Lec ?