SUB MAIN QUESTIONS. ADVICE NEEDED

[plugsandsparks]

I had thought

I had thought about a TPN board, but was wary of the fact one of the DBs the 25mm armour feeds has a 10mm shower circuit, 10mm induction hob circuit, 2 ovens, few rings circuits, few lightening circuits etc. So 63A on the armour may not be acceptable?

Do MCBs not go upto 63A max? Would the above load on the DB not potentially pop the 63A? MCCB panel sounds more appropriate as you can use the 80A MCCB to give it some more juice, but it must’ve been too costly for the client, and that’s why the spark had bought the 80A switched fuses

Dunno, thats where design comes into play. To expand on the similar install. Although it was TPN in the plant room, because of the length of cable runs and TP loads, I had TPN board in plant room, submain TPN board on first floor, feeding 2 SPN submains also on first floor, TPN board in garage (submain off plant room) so for the house there were 5 DBs in total (and they were all stacked) - I think your concern about loading one phase up to 80A and they having a heat pump at 50A (bearing in mind how long there cycle is) maybe a bigger issue. Anyway its all about the design...

 

[westward10]

Cost! they own a mansion.

 

[Nelly72]

Cost! they own a mansion.

I know, you know how people behave sometimes tho lol

 

[pc1966]

You get some 250A TPN boards that take a mix of wide 80-125A MCBs, and normal (17.5mm width) <= 63A MCBs from Hager. But you won't get decent selectivity that way with downstream DBs.

Going for a MCCB board would be the best option as then a incoming switch for all, and easy choice for any out-going protection from tens of amps upwards, along with reasonable (typically kA-range) selectivity on faults. Ideally put your SPD in there.

Fuses are good in many cases, but a busbar chamber and switched-fuses coming off is a bit of work and not likely cheaper than MCCB board, and MCCB boards are far easier for anyone to reset or to isolate stuff as needed,.

 

[buzzlightyear]

have you taken any picks of the main board so we can establish what is needed ,

 

[buzzlightyear]

what is the DNO SET UP .is there a main DB or just feed from H blocks .

 

[Mike Johnson]

Use a main Three phase RCD CU to distribute a single phase to each floor/main area with a separate CU, at 100amps/phase it's not going to be a problem.

 

[westward10]

What is a main three phase RCD CU?

 

[nicebutdim]

All three lines protected by a single RCD? Seems less than ideal.

 

[Mike Johnson]

What is a main three phase RCD CU?

Just a CU with a three phase RCD to supply the three phase air pump and to distribute the single phase's to the other CU's.

All three lines protected by a single RCD? Seems less than ideal.

Each subsequent CU to have a single phase RCD or as many as you want.

 

[westward10]

Never seen a three phase CU and the pump is not likely to need an RCD.

 

[Rockingit]

Why not just put a 6 way Ryefield downstream of the DNO incomer? Gives you a box to gland into, choice of fuse sizes and a better disconnection time. 2 ways for the subs, 3 ways for the plant room (which I'm assuming will need a 3ph board in it regardless) plus a spare for the future.

 

[westward10]

Sounds like the client has already obtained the parts so other options are not likely to be favoured.

 

[westward10]

Just a CU with a three phase RCD to supply the three phase air pump and to distribute the single phase's to the other CU's.


Each subsequent CU to have a single phase RCD or as many as you want.

Mcbs are not likely to achieve selectivity. Using such devices for distribution is a poor design.

 

[Rockingit]

Sounds like the client has already obtained the parts so other options are not likely to be favoured.

Something about the blind leading the blind. At £90 a pop, plus all the other Henleys, Tails, time.... small MEM board would be cheaper!!

 

[plugsandsparks]

Came across a TP board with a RCD where one would normally find a 60947-3, thought that was odd. Then about a month later found another one, it must have been a thing 20-30 years ago. Think they were MEM boards but cannot be sure.

 

[Mike Johnson]

It's how I was instructed to do it by the French "Conusule" who are the regulating body in France, the incoming main is into a S type RCD at the meter this is EDF equipment you have no choice.

 

[DPG]

It's how I was instructed to do it by the French "Conusule" who are the regulating body in France, the incoming main is into a S type RCD at the meter this is EDF equipment you have no choice.

Luckily the OP is not in France.

 

[plugsandsparks]

Makes Sense, although these were in the UK and well downstream of the DNO head and pretty sure they were not S type but cannot be sure BUT there were no RCDs on the final ccts. It all looked strange to me

 

[plugsandsparks]

There is still one on a site i go to occassionally will try and get a photo.. as i would like to know if its was once a thing.....