Two ovens and a hob...

[BlackStuff]

Hi, could do with a bit of advice please...

I'm in the process of fitting out a kitchen for a small sandwich shop. This has two fan ovens mounted side by side in a fitted cupboard, with a gas hob over one of them.

Each oven is rated 13A so it is my intention to run a 2.5mm ring main via three fused spurs above worktop level, one for each oven and one for the hob, and feed the lot via a 30A MCB.

Q1. Is it ok to run two ovens off the same circuit in this way?
Q2. Can anyone recommend a neater solution for the "above decks" bit, other than having 3 single switched spurs which is going to be a pain to tile round? I can easily mount any size of box as I've got a plywood panel here stood off the wall on battens so can easily cut holes and feed cables behind etc. I'm wondering whether to put a 6 gang gridswitch in with a row of 3 switches above a row of 3 corresponding fuses...
Q3. What does everyone generally use to put in the back of the enclosed cupboards to connect the oven and hob flexes into? Is a standard MK cooker outlet ok and a 13A socket for the hob ok? (I'm worrying about the heat behind the ovens).

On a related topic...
Q4. I'm fitting a dishwasher under the sink drainer. Again I plan to fit a fused isolator above controlling a 13A socket below. How high above the sink does the isolator have to be, given that I can't really get it more than about 18" away from the tap horizontally?

As regards building control, I am a competent time served electrician, just a bit rusty on the regs as I haven't worked in the trade for a while. I am informed by someone who is "current" that I need not worry about Part P / Buildings Control as this is not a domestic installation, and I'm not getting paid for doing the job (it's my own shop). Does everyone agree or am I going to get my collar felt!!!!

Any advice mucho appreciated...

 

[Steve]

1. Dont use a ring main. A 32 amp radial in 4mm will be fine. A ring main is not designed for use where all the load is in one place.

2. 6 gang Gridplate, 20 amp gridswitch, 3 gang mounting frame (you'll need 2 of these), 13 amp grid fuse, 6 or 8 gang grid box

Everything you need to create 3 FCUs in one box

3. There shouldn't be any heat behind the ovens. The oven heats its cavity, not the space around it. The best way, IMO, with remote fusing, is to use 15A unfused plugs and sockets.

4. The switch can be 2 metres from the appliance, but its purpose should be obvious. Just mount it 30cm from the sink drainer.

Part P doesn't apply to commercial premises, but legally, you should have public liability insurance. If anything goes wrong, and a member of the public is injured, its you who will have to pay.

 

[BlackStuff]

Thanks for the help.

1. Dont use a ring main. A 32 amp radial in 4mm will be fine. A ring main is not designed for use where all the load is in one place.

Actually I've now checked and the ovens are only rated 1KW each, so I can run a single 2.5mm spur fed from a 20A fuseway and then fuse each one at 5A, thus saving me from buying a reel of 4mm cable!

2. 6 gang Gridplate, 20 amp gridswitch, 3 gang mounting frame (you'll need 2 of these), 13 amp grid fuse, 6 or 8 gang grid box

Everything you need to create 3 FCUs in one box

Great stuff. Just been out and bought exactly that!

3. There shouldn't be any heat behind the ovens. The oven heats its cavity, not the space around it. The best way, IMO, with remote fusing, is to use 15A unfused plugs and sockets.

4. The switch can be 2 metres from the appliance, but its purpose should be obvious. Just mount it 30cm from the sink drainer.

Just to confirm, 30cm above the drainer is ok? The horizontal separation from the sink isn't an issue?

Part P doesn't apply to commercial premises, but legally, you should have public liability insurance. If anything goes wrong, and a member of the public is injured, its you who will have to pay.

I have public liability insurance for the premises anyway, so I'm happy with that angle. I just wanted to be sure I wasn't invalidating it by actually breaking any laws; like (I think) I would be if I connected the gas hob myself...

 

[Steve]

I wonder how long these 1kw ovens take to warm up? And how many DIYers STILL fit them on grossly overrated circuits! But thats a subject for another day . . .

The FCU for the dishwasher - just use common sense. Dont put it where it will be splashed in the normal use of the sink. I'd fit it on the same level as the other accesories, but a bit further along, say at the edge of the sink drainer. This will be sufficient distance from the sink, IMO.

For example, this is not sufficient distance:

Yes, this is a commercial premises too and that box gets splashed quite a bit when the boiler tap (and the cold tap for that matter) is running . . . And theres no local isolation, though its on a timer to shut off at night.

 

[BlackStuff]

I wonder how long these 1kw ovens take to warm up? And how many DIYers STILL fit them on grossly overrated circuits! But thats a subject for another day . . .

The FCU for the dishwasher - just use common sense. Dont put it where it will be splashed in the normal use of the sink. I'd fit it on the same level as the other accesories, but a bit further along, say at the edge of the sink drainer. This will be sufficient distance from the sink, IMO.

Sounds reasonable. There won't be a cable outlet from it so the splash risk is pretty minimal anyway.

For example, this is not sufficient distance:

Yes, this is a commercial premises too and that box gets splashed quite a bit when the boiler tap (and the cold tap for that matter) is running . . . And theres no local isolation, though its on a timer to shut off at night.

That's a classic! Mind you I can perhaps go one better. I bought my last house new, and one of the snags I had to get resolved when we moved in was a 2 gang 13A socket mounted so close to a sink that if you swung the mixer tap round it was directly above it! The builders rep was game though - when I demonstrated this to him he said it was ok as no-one would reasonably swing the tap round away from the sink in this way. Clearly he didn't have children...

Anyway, back to the job in hand: I've slotted it all in now and the grid switch solution looks really neat - tons better than a row of 3 or 4 FCUs. Mind you, so it should - it cost enough! I used an 8 gang one in the end with the fourth Fuse / Switch pair isolating the overhead extractor, and by the time I'd totalled all the bits up it was over £60!!!

Next question:

The shop is currently fed by the ubiquitous Wylex 6 way consumer unit. For obvious reasons I'm upgrading this to a split load one with a 30mA RCD. What (if anything) do the regs currently say about which circuits must be fed via the RCD?

 

[Steve]

In a sandwich shop, i dont think any circuits NEED to be RCD protected, unless you might be using portable appliances outdoors, which I doubt.

Fit a standard CU, no RCD, and if you need to in future, you can add RCBO protection.

Definitely dont put any freezer or fridge circuits on an RCD, the same goes for the ovens.

 

[davy_owen_88]

In a sandwich shop, i dont think any circuits NEED to be RCD protected, unless you might be using portable appliances outdoors, which I doubt.

Fit a standard CU, no RCD, and if you need to in future, you can add RCBO protection.

Definitely dont put any freezer or fridge circuits on an RCD, the same goes for the ovens.

I'm not sure if this applies to commercial installations but if you are on a TT supply you will need a 100mA RCD protecting everything. Maybe the 30mA RCD could be omited?

 

[Steve]

In a sandwich shop, i dont think any circuits NEED to be RCD protected, unless you might be using portable appliances outdoors, which I doubt.

Fit a standard CU, no RCD, and if you need to in future, you can add RCBO protection.

Definitely dont put any freezer or fridge circuits on an RCD, the same goes for the ovens.

I'm not sure if this applies to commercial installations but if you are on a TT supply you will need a 100mA RCD protecting everything. Maybe the 30mA RCD could be omited?

oops. apologies. Indeed if you have a TT supply, you will need at least a 100mA overall RCD, which can be fitted as the main switch. If you do have a TT system, might be worth a phone call to the DNO to get it changed to PME, while you're doing this work.

 

[BlackStuff]

Thanks for the info guys, sorry for not getting back sooner. Supply does have an incoming earth so no need for an RCD, though I may but an individually protected socket by the door in case we end up using some outside equipment in the future.

As an aside, had a strange experience tonight. Was working away this afternoon when the supply failed, which wasn't totally unexpected bearing in mind the weather we've been having. Gave up and went home!

However, went back at about 6pm and supply appeared to have been restored, except that when I went in the shop the emergency lights were still on and the main lights (flourescent) wouldn't fire up. Turned on a light in the back room which was a filament bulb and that lit, though dimly. God knows what the voltage actually was but it was nowhere near 240!

Curiouser still, just called round there again now to find that the filament lamps appear normal brightness but the flourescents still won't do anything more than flash every few seconds. I'm wondering now whether the frequency is down rather than the voltage. I've seen some dips and "brown outs" in my time, but nothing this severe or prolonged. I can imagine any motorised equipment could be running into severe overheating problems.

 

[plugwash]

i'd imagine frequency problems are very rare, the whole grid has to run in lockstep and i belive the frequency deviation that will cause the grid to start emergency load shedding is pretty small. I belive grid control places have frequency displayed to something like 5 decimal places!

i guess you don't have a scope you can hook up to see whats going on do you?

 

[Sarahspark]

Are the fluorcescents fitted with electronic starters that could have possibly been damaged by a voltage surge

Sarah