My last 'non Amd 3' CU Install.

[Dave OCD]

Put this in today, I hope it doesn't burst into flames.:tongue3: Didn't have the time to faff about and get the cabling 'perfect' as I had so much to do today but I think it's ok. With the BG boards I generally 're number' the earth bar as to me it's illogical having the CPCs running in the opposite order of the neutrals,I'll miss the insulated CUs. Sorry about the
poor photo.

 

[sparksfly]

Ok thanks fore the response. I guess my tutor just had his opinion regarding this then.

I agree with darkwood.....in a domestic situation there are generally no issue with regards to MCB order. The majority of domestic real world situations (unlike the neat cu examples here....( i like the wallpaper BTW,it blends in !!)...maybe MK should not have pre-cut holes) When I take the cu cover off...Im greeted with a full birds nest of wires. Its easier to add a new shower circuit on the end as opposed to rearranging previously installed MCBs.
Dont get me started on the CU metal jacket theme....its just loose wires, cheaper terminations or bad work.....I was going to make some deep plasterboard picture frames to cover the cu.........hey ho.... I ve just put me angle grinder in the van for 2016.

 

[Simonslimline]

Its common practice to load the heavy breakers first then the lightest loads last, I have not in my years been given a logical reason as to why and yes! I was also taught that way in the 80's. I wouldn't worry about order too much in domestic but like I said when stepping into other types of industry with heavier switchgear and loads then this advice becomes misleading and can cause premature tripping, overheating etc etc. I would be interested if your tutor can give a valid reason, putting a heavy load on the end will not reduce the momentary voltsdrop as the load is energised - if you suffer the lights flicking when you switch the kettle on etc then changing the mcb order will not reduce it as its a VD on the supply itself as it adjusts to the new load.

He is retired now so no chance of asking. I expect he was taught it as well.

Thanks for the info.

 

[Deleted member 9648]

Well we sussed out the wallpaper border and fixing it to the water pipes, what's the third?

Try the main earth through a different entry to the tails in the metal board.
(and, no....I'm not posting one of mine!)

 

[davesparks]

Its common practice to load the heavy breakers first then the lightest loads last, I have not in my years been given a logical reason as to why and yes! I was also taught that way in the 80's.

As it was told to me:

Once upon a time, before Wylex invented the modern CU as we know it you had to put your own wire links in to join the live side of the fused together. This was done by daisy chaining from one fuse to the next, so to allow progressively smaller sizes of wire along the links and to reduce the number of connections carrying higher currents they started with the biggest fuses and went down to the small ones.

Also I believe the very early consumer units had higher rated fuseways next to the main switch than they did at the end of the row.

 

[Deleted member 9648]

As it was told to me:

Once upon a time, before Wylex invented the modern CU as we know it you had to put your own wire links in to join the live side of the fused together. This was done by daisy chaining from one fuse to the next, so to allow progressively smaller sizes of wire along the links and to reduce the number of connections carrying higher currents they started with the biggest fuses and went down to the small ones.

Also I believe the very early consumer units had higher rated fuseways next to the main switch than they did at the end of the row.

Not heard that one, I always assumed it was to keep the heaviest loads close to the incomer.....although it always seemed a bit pointless.

 

[Midwest]

Try the main earth through a different entry to the tails in the metal board.
(and, no....I'm not posting one of mine!)

It could be hiding behind the tails through the stuffing gland?

 

[bigspark17]

Try the main earth through a different entry to the tails in the metal board.
(and, no....I'm not posting one of mine!)

Reg number aggainst that? And your views on why you think its dangerous?

 

[Midwest]

Seem to remember we had hundred + post debate about that one, a short while ago. I can't be arsed to locate it though. Sure someone who's really bored will pop along with a link shortly

 

[davesparks]

Reg number aggainst that? And your views on why you think its dangerous?

I don't have a regs book to hand, but it has been a long standing regulation that all conductors of a circuit, including protective conductors, must only be collectively enclosed by ferrous metal.

The reason is to prevent eddy currents from occurring in the ferrous metal. Under fault conditions a massive current can flow through the protective conductor, which in turn would induce massive eddy currents if it passes through a different hole to the respective line conductor.

 

[Deleted member 9648]

Reg number aggainst that? And your views on why you think its dangerous?

Only book I have to hand is the BRB.....521.5.2. May have changed reg number in the new amendment.
Unlikely to be dangerous in a small CU but still against regulations on electromagnetic effects.

 

[davesparks]

Only book I have to hand is the BRB.....521.5.2. May have changed reg number in the new amendment.
Unlikely to be dangerous in a small CU but still against regulations on electromagnetic effects.

You're doing better than me, ive only got 13th 14th and 16th to hand at the moment

 

[shanky887614]

how would an earth cause a problem when it is at the same potential as the enclosure? unlike between L,N etc which are at a different potential to earth

 

[Simonslimline]

how would an earth cause a problem when it is at the same potential as the enclosure? unlike between L,N etc which are at a different potential to earth

Current under earth fault conditions.

 

[davesparks]

how would an earth cause a problem when it is at the same potential as the enclosure? unlike between L,N etc which are at a different potential to earth

As per #162 when current flows through the protective conductor it will create eddy currents if the respective live conductors are not in the same hole.
Conventional wisdom says eddy currents become apparent at around 200A and above, th ecurrent in a protectove conductor, especially at the origin can be in the order of thousands of amps

 

[shanky887614]

As per #162 when current flows through the protective conductor it will create eddy currents if the respective live conductors are not in the same hole.
Conventional wisdom says eddy currents become apparent at around 200A and above, th ecurrent in a protectove conductor, especially at the origin can be in the order of thousands of amps

we are talking a sub 100amp single phase house supply here where the biggest supply will probably be a shower at 50amp.

with the new reg of all circuits on rcd's im not sure how many decades of leakage it would take to cause any issues on a small domestic property without tripping an rcd if it shows any signs at all