SUB MAIN QUESTIONS. ADVICE NEEDED

[Nelly72]

Hi all.

I have been asked to take over a job an electrician has started, and has moved abroad.

The house is a big mansion, with a 3PH supply, with 100A fuse on each Phase.

The electrician has ran 2 25mm 3core armours to another 2 DB’s in the mansion, and there has to be a DB fitted where the incoming supply is, bringing it to a total of 3 DBs.

In the plant room, there is also a 3PH heat pump.

However, my question is how would you all terminate the sub mains. Would you bring each phase into a Henley block, and branch off into a 80A switched fuse for the armour sub mains, and take a tail off the Henley blocks for each phase into a separate enclosure with a protective device for the heat pump, or would you fit a TPN board, and bring all armours into it + the heat pump supply?

If it’s a TPN board would you fit MCBs or MCCBs for the 25mm armours? Is there even

I’m a new build house basher, so this is abit more complex to what I’m used to, even though it’s a new build, so please go easy on me I am simply just wanting advice to keep me right.

 

[plugsandsparks]

Reminds me of a large house i did, very similar. Used TPN board in plant room and fed all local loads and submains from that board. Submains were C63 MCBs, GSHP C50 from memory. As mentioned one isolator for whole property, easy to expand and does not take up huge space with fused submains.... who uses fuses nowadays, lol.

 

[Nelly72]

There is nothing wrong with this but it looks a bit "housebasher", apologies for this. When I do a job I like to look back and think that is a good job rather than not look back knowing there was a better more professional way. What about surge protection?

Can they not be fitted at each DB to protect all appliances ?

 

[westward10]

Personally I would run the heat pump from a switch fuse.

 

[Nelly72]

I had thought

Reminds me of a large house i did, very similar. Used TPN board in plant room and fed all local loads and submains from that board. Submains were C63 MCBs, GSHP C50 from memory. As mentioned one isolator for whole property, easy to expand and does not take up huge space with fused submains.... who uses fuses nowadays, lol

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

 

[Nelly72]

Don't think you can run tails directly to a 3 phase MCB for the heat pump, would need some kind of main switch as well wouldn't it. Why not fit a small 3 phase board for DB3 and run the heat pump from there, maybe a type A board if it doesn't need to be too big.

Oh and BTW I've taken over the odd job over the years where the original electrician "has gone AWOL" one time he supposedly "went abroad to learn sky diving", another time the spark had "broke his leg". But those jobs had one common denominator, getting paid was a pain in the arse. Make of that what you will.

Yeah that was my plan, a small board with a main switch/mcb, then out to a rotary isolator..

My sketch was a bit misleading

 

[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.