Adjusting tripping time.

[An Buachaillín Bán]

Hi all,

Curious one and hopefully some one of you could give me some advice.

A customer has had a steeltech shed installed at their premises. A large one. Wants 3x light fittings and 5 double sockets intalled. There's an electric roller shutter door on the shed also to be plugged in. My plan was to run a 6sq cable out from house DB, and put a little enclosure in shed with rcbos for lights and sockets, all backed up by a 32 or 40A mcb at house DB.

Customer stated that because the electric roller shutter is the only means of accessing the shed, that in the event of a power failure he'd have to smash a window to get into shed to open the shutter manually from the inside. And so he's requesting if there's any way the power in the house DB would trip first rather than the shed DB in event of power failure to shed. Hope this makes sense.

Any advice would be much appreciated in how to approach this

 

[DPG]

This is the problem of an electric door being the only means of access. Is there no way they could have a pedestrian door added?

What are they going to do in the case of a power cut, or if the motor start capacitor fails?

 

[An Buachaillín Bán]

This is the problem of an electric door being the only means of access. Is there no way they could have a pedestrian door added?

What are they going to do in the case of a power cut, or if the motor start capacitor fails?

I know. It makes no sense to me to not have a door there. If there's no way around it, it might be the only option.

 

[diditrain]

Is there definitely no manual override on the door?

 

[OLDBOY]

It would be difficult to arrange a constant power supply to the door but you could minimise any tripping risk by feeding the shed from a fused isolator at the supply end via henleys rather than an mcb from the house db. Then feed the door itself from an mcb rather than an rcbo, clearly though the door will have to be hard wired not plugged in.

 

[An Buachaillín Bán]

Is there definitely no manual override on

There is. But on the inside only

 

[plugsandsparks]

Or just supply the roller door from a suitable UPS, have seen this done for gates but not for roller doors as there has been to date, a pedestrian access door. This is really a major oversight......

 

[timhoward]

I've seen several issues with roller-shutter doors. Motor failure, mechanical failure, switch-gear failure, even seen one struck by a vehicle and be stuck open.
I've never known a power supply failure and it's unlikely to be the big problem that causes a lock-out. As already suggested a UPS covers that base, but honestly there are so many other things that could cause him to be locked out. The whole concept needs looking at again.

I've seen some garage doors that have a flexible shaft connected to an axle that sticks through the wall, so they can be wound from outside. It's got to be worth at least talking to the door manufacturer about the issue and seeing if they have any easy answers.

 

[OLDBOY]

TBH none of the above is the OP's problem. On many ocassions I have felt obliged to try and talk a client out of a daft idea, usually unsuccessfully. He must know what is going to happen on a power failure, if he wont listen, then my suggestion will pretty much eliminate the possibility of the supply to the door itself failing, the rest is up to him.

 

[newfutile]

I suppose you could have some type of reverse selectivity / discrimination by running it in over size cable and ocpd bigger than the supply , but the internal wiring would not be protected by say a 50amp mcb and the time current curves would still overlap.
it also would not pass a fire risk assessment.
we all know anything mechanical will fail , in my opinion a door of some time is necessary.

 

[An Buachaillín Bán]

Or just supply the roller door from a suitable UPS, have seen this done for gates but not for roller doors as there has been to date, a pedestrian access door. This is really a major oversight......

Interesting. UPS system would be one way out of his predicament alright. Having spoken to the client yesterday he stated that he's happy to continue as normal, and that in the event of a power failure, he will just have to break the window. I can't imagine it happening too often, or power cuts lasting too long. Oversight is right though!

Edit: actually in hindsight, I realise how silly my initial comment was where I asked if there was any way the mcb at house DB would trip first before the shed. But if the shed is fed from house DB, then if it trips there'll be loss of power anyway. Apologies.

 

[DPG]

Interesting. UPS system would be one way out of his predicament alright. Having spoken to the client yesterday he stated that he's happy to continue as normal, and that in the event of a power failure, he will just have to break the window. I can't imagine it happening too often, or power cuts lasting too long. Oversight is right though!

Just make sure nobody ever fits security bars to the window eh

 

[An Buachaillín Bán]

I've seen several issues with roller-shutter doors. Motor failure, mechanical failure, switch-gear failure, even seen one struck by a vehicle and be stuck open.
I've never known a power supply failure and it's unlikely to be the big problem that causes a lock-out. As already suggested a UPS covers that base, but honestly there are so many other things that could cause him to be locked out. The whole concept needs looking at again.

I've seen some garage doors that have a flexible shaft connected to an axle that sticks through the wall, so they can be wound from outside. It's got to be worth at least talking to the door manufacturer about the issue and seeing if they have any easy answers.

I'll get him to contact the installer. Surely as you say this isn't an issue that hasn't cropped up before. Thanks

 

[davesparks]

Put the roller shutter on its own circuit in the garage CU, that way it will only trip if the roller shutter becomes faulty (assuming the wiring is installed to a good standard and protected from likely sources of damage).

Or add a lock/handle which can be opened from the outside to the window.

 

[OLDBOY]

Put the roller shutter on its own circuit in the garage CU, that way it will only trip if the roller shutter becomes faulty (assuming the wiring is installed to a good standard and protected from likely sources of damage).

Or add a lock/handle which can be opened from the outside to the window.

Not if the OCPD at the supply end is an mcb. A fault on any final circuit in the garage which would trip an mcb at the garage end will probably take out the supply mcb as well.
Another potential issue the OP may face is the type of building....steel construction?
If so this may result in a TT being required if the supply is TNCS as the OP states a 6.0mm distribution circuit. That would considerably increase the possibility of nuisance tripping.