tower scaffolding near 240v overhead wires - what's the risk analysis?

[Jim K]

Three wires come to the house from a pole in the garden, they are 240v. they have black plastic looking insulation on 2 of the three (I presume the other unsheathed is earth?). The wires are at an acute angle to the wall in question.

I need to get to the chimney stack with (ideally) a tower scaffold which would come close to the wires as it ascends past them.

How close is sensible? how to analyse/rationalise risks?

or Can I build a scaff tower slightly offset from the line of the stack (i.e. a bit further away from the wires) and then *somehow* arrange some safe scaffolding around the stack itself?

thanks for any (constructive;>)) thoughts

Cheers Jim K

[Jim]

The power company came out and put yellow sheathing round our power cables for free when we had a bunch of deliveries last year via HIAB lorry.

[Dave Liquorice]

Yep, scaffold company arranged that for us before the scaffolding went up last week.

[Bob Minchin]

If it is going to be just you going up the scaffold then common sense is the rule. If you want - slip some pipe insulation over the cables but not really necessary tbh.

If you are asking others working for you to go up there then commercially erected scaffolding will (should!) cover you from a risk point of view as they will have an accepted procedure compliant with their insurance.

Bob

[js.b1]

Also, consider asking for a glass fibre scaffold tower. They exist and in some cases are no more expensive (because they are not hired out often).

[Andrew Gabriel]

As others have said, get them sleeved for free by the power company.

Back when ogrish.com still existed, many pictures of smoldering bodies as a result of contacting overhead lines with scaffolding (although mostly higher than mains voltage).

[Jim K]

do they come out and remove it too? were your wires "bare" before they did that? what did they do where the wires met the building? - we have a "3 pole bracket" for want of a better descrip....

Did your scaff rub touch the wires? go near them (how near)?, straddle them?, something else?

Cheers Jim K

[Andy Dingley]

In some places they're the only sort you can get - Scousers will nick the aluminium ones overnight!

[Dave Liquorice]

I hope so...

We only have two incoming wires, the "live" is insulated, but it's not very thick, really only to prevent casual contact rather than any form of robust protection. The "neutral/earth" is bare copper.

The sleeves cover up to the insulator a bit of tape was wrapped around the join between the cable running into the house and the overhead line.

The scaffold (as installed) is clear of the cables. The cables do cross a riser at about 4', clearing of the top of the guard rail by about a foot. The sleeve being quite large 30 mm dia with a 20 mm yellow flash below makes them far more obvious when moving about on the riser.

[Jim]

It was the wire going down the road which we were protecting from lorry mounted cranes - the scaffolding associated with our extension didn't come close to where the wires came into our house and as a matter of fact we've now done the work to bring the wire into a meter cabinet via an underground trench.

The sheathing hasn't actually been removed yet.

[Dave Liquorice]

At this point in our supply the wired pole fuse is 200A. 48kW makes for a at lot of energy to be dissipated before the fuse even thinks about going pop...

Would the auto-recloser on the 11kV detect the "fault" on the 240v side? After all there would be more power going than coming back as some would be going via the real earth. All the same that auto-recloser puts the power back on 3 times before locking out.

[Jim K]

intellisting ta

how quick did they come out and do the sheathing from when you asked? do they do it with long poles or something else "pedestrian based" ? or something else?

Cheers again

Jim K

[Dave Liquorice]

About a week but I didn't arrange it the scaff company did and I think they have direct contact with the boys that do the work, rather than going through "customer services".

Up a ladder against the wall where the cables are attached.

[Jim K]

many thanks Dave CHeers Jim K

[alexander.keys1]

HRC fuses generally have a 'fusing factor' of 1.5, meaning 300A (72 kW @ 240v) will need to flow before it blows rapidly.

It wouldn't detect an earth fault on the LV side, because the fault current would return to the LV neutral point, same as load current, unless possibly it was of very low impedance, amounting to a L-N short close to the transformer.