Student accomodation

[Jayjay2324]

Morning all!

I past a job onto a friend of mine which was rewire what was a 2 bedroom semi into being refurbished into a 5 bed student house. I suggested just wiring simple ring mains but that's because it turns out I am simple.

So his suggestion is to wire each room individually, as 4mm twin and earth radials protected by a 32A rcbo. Only 5-6 twin sockets in each room but he reckons 4mm just to cover things as we don't know if these students will have their own irons, kettles, toasters, heaters, mini fridges etc in their rooms. The house will have central heating but just in case which I think is perfectly ok...correct me if I'm wrong though.

The thing that I'm not sure of though is that he mentioned sticking a unswitched spur at the end of each radial in the room (wired in 4mm) and wiring the light for that room off it, protected by a 3A fuse wired in 1.5mm twin and earth. I mean although its only a single 6'' ceiling rose with a 24w energy saving lamp, is this ok to do?????

I understand what he is saying as each room can be isolated in case of fault of maintenance etc but the lighting I'm just concerned about.

Any advice welcomed and many thanks in advance.
I'll try to reply back to any questions and comments as soon as i get back tonight. Thanks

 

[PrenticeBoyofDerry]

Having a 4.0mm2 T&E radial on 32A device, is what it should be.
Having a lesser cable CSA could lead to cable becoming overheated on 32A.

To me the wiring would depend on whether the rooms are individually metered for consumption.

I don't think having only one circuit for both sockets and lighting is a good one, if the RCBO trips, the poor bugger has no lights and no socket to plug a lamp in.

 

[bernardgreen]

The idea of each room having its own radial is a good one. 32 amps for a single room is a bit high, ( potential for large electrical bills ). 16 would prevent excessive use od electricity.

The lights should not be fed from the radial as an accident that trips off the radial would leave that room in darkness.

Students can create some horrendous accidents when they mis use electrical equipment in a student house.

 

[Jayjay2324]

The idea of each room having its own radial is a good one. 32 amps for a single room is a bit high, ( potential for large electrical bills ). 16 would prevent excessive use od electricity.

The lights should not be fed from the radial as an accident that trips off the radial would leave that room in darkness.

Students can create some horrendous accidents when they mis use electrical equipment in a student house.

I think 16A on a 2.5mm radial for each room is a bit risky just in case they do run heaters mini fridge irons etc? Or am I just being over cautious?
Agreed though that the lighting should be wired seperate

 

[winston1]

The idea of each room having its own radial is a good one. 32 amps for a single room is a bit high, ( potential for large electrical bills ). 16 would prevent excessive use od electricity.

The lights should not be fed from the radial as an accident that trips off the radial would leave that room in darkness.

Students can create some horrendous accidents when they mis use electrical equipment in a student house.

I think 16A on a 2.5mm radial for each room is a bit risky just in case they do run heaters mini fridge irons etc? Or am I just being over cautious?
Agreed though that the lighting should be wired seperate

Basically agree with the above, but a compromise would be 20A on a 2.5mm radial.

Lighting does not need 1.5 mm cable, use 1.0mm.

 

[ericmark]

My first reaction was to say no. But as I consider it there is no difference to supplying a caravan from a single RCD to everything in a room off a single RCD as long as a window in the room.

We are told we have to used two RCD's one feeding the next to supply caravans and boats so I can't really see a problem. Personally however I would not include lights.

And since treating like a caravan then why not same supply as you would use for a caravan 16A is ample.

If really worried about lights could used emergency lights so should a student trip the RCBO then not plunged into darkness.

 

[Jayjay2324]

Do you guys think a 20A radial supply would be sufficient enough for all these things mentioned? Desktop computers, hairdryers, iron, mini fridge, heater just in case, hoover etc??? Obviously by applying diversity but Tbh I've never sat and worked it out. I should give it a will go tonight.
yes definitely agreed with him to wire lighting seperate now but just thinking if we can save money wiring socart supplies in 2.5mm rather then 4mm we would save a hell of a lot of money.

Having to wire emergency lighting on hall, stairs and landing but I've advised to wire them on their own supply aswell.
Thanks a bunch so far.

 

[JohnW2]

Do you guys think a 20A radial supply would be sufficient enough for all these things mentioned? Desktop computers, hairdryers, iron, mini fridge, heater just in case, hoover etc???

Presumably not if all those things you mention were used simultaneously, so you have to make a judgement as to what is 'likely' (probably for 'long periods of time', since that's the language which the regs usually use).

It is, of course, not actually a 'safety' issue, per se. Provided the MCB is appropriate for the cable, in the case of overload it will trip before any harm comes to the cable - that's the whole idea of having it. However, the circuit should still be designed on the basis of what you judge to be the 'likely' maximum load, whatever you feel that actually is.

Kind Regards, John

 

[Jayjay2324]

I've had a quick workout of appliance wattage for a worst case scenario as-

fan heater - 2000w @8.3A
iron - 2000w @8.3A
hoover - 1500w @6.25A
straighteners - 300w @1.25A
hair dryer - 1200w @5A
mini fridge - 120w @0.5A
desktop computer - 200w @0.83A
32'' plasma tv - 400w @1.67A
dvd player - 60w @0.25A
games console - 200w @0.83A
phone charger - 10w @0.1A

TOTAL - 7990 watts @33.28A

Keeping fan heater at 100% and applying 40% to the other supplies = 24.98watts @9.92A + 8.3A = 18.29A???

Is this correct? So wiring the radials in 2.5mm twin and earth should be ok unless you chaps can think of anything I've missed or cocked up.

 

[JohnW2]

I've had a quick workout of appliance wattage for a worst case scenario as- ..... TOTAL - 7990 watts @33.28A .... Keeping fan heater at 100% and applying 40% to the other supplies = 24.98watts @9.92A + 8.3A = 18.29A???

In terms of the likely average over any reasonable period of time, that is actually very 'pessimistic'. The fan heater is not going to be on for 100% of the time, and most of the other 'major' items (hair dryer, straighteners, hoover and even iron) will only be on for short periods of time, far less than 40%. On the other hand, there may well be short periods during which several of those things are being used simultaneously, so the 'instantaneous maximum' could be appreciably greater. Any such calculations are necessarily probabilistic, essentially based on guesswork.

Is this correct? So wiring the radials in 2.5mm twin and earth should be ok unless you chaps can think of anything I've missed or cocked up.

As I said in my previous post, if the MCB is appropriate for the cable (probably 20A), the cable cannot come to any harm - the worst that happens is that the MCB trips.

Having said that, the marginal difference in cost between 2.5mm² and 4mm² cable is not that great and with the latter you could probably have a 32A circuit (32A MCB).

Kind Regards, John

 

[SimonH2]

Another way to look at it ...
If you are worried about tripping a 20A MCB because of the loads, consider the potential if you fit 32A MCBs. 5 rooms, 32A MCB each, that's 160A - what's your main fuse rated at ?

Unless it's a very very cold house, running more that 5kW (supported on a 20A circuit) for any length of time is going to leave a room well and truly sweltering. So I can't see much need for more than 20A.

I recall back when I was at uni we had metered sockets - 2 in the whole room IIRC ! But we also had (in the older rooms) one or two 2A sockets on the lighting circuit (not metered). Needless to say, being a bit of a tight-a**e, I worked out how much I could run on 2A - which included a 500W immersion 'kettle' I found at Woolies.

 

[OwainDIYer]

iron - 2000w @8.3A
hoover - 1500w @6.25A

In a student house?

 

[phatboy]

iron - 2000w @8.3A
hoover - 1500w @6.25A

In a student house?

 

[ban-all-sheds]

I've had a quick workout of appliance wattage for a worst case scenario as-

fan heater - 2000w @8.3A
iron - 2000w @8.3A
hoover - 1500w @6.25A
straighteners - 300w @1.25A
hair dryer - 1200w @5A
mini fridge - 120w @0.5A
desktop computer - 200w @0.83A
32'' plasma tv - 400w @1.67A
dvd player - 60w @0.25A
games console - 200w @0.83A
phone charger - 10w @0.1A

TOTAL - 7990 watts @33.28A

Keeping fan heater at 100% and applying 40% to the other supplies = 24.98watts @9.92A + 8.3A = 18.29A???

Is this correct? So wiring the radials in 2.5mm twin and earth should be ok unless you chaps can think of anything I've missed or cocked up.

How many people live in each of these rooms?

5? 6?

You are postulating the simultaneous use of an iron, a hoover, hair straighteners, hair dryer, PC, TV, DVD player and games console. Either the room is heaving with people shouting at each other over the din and not generating enough body heat to negate the need for a 2kW fan heater, or the person living there is taking enough speed to kill Lemmy.

 

[ericmark]

At 6A with caravan and narrow boat I have tripped the MCB. At 16A I have not tripped the MCB even with three adults and two children in the narrow boat and caravan. At 63 foot long even if only 6 foot wide the living area in a narrow boat must exceed the area of most student rooms. Plus your talking about 20A not 16A.

Even if it does trip still easy for the student to reset so I would go for 2.5mm cable and B16 trips. As you say could use B20 trips but no real need to exceed that.