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Lead-insulated conductors #195473 08/04/10 09:53 PM
Joined: Aug 2009
Posts: 13
SactoCliff Offline OP
Member
Anyone have experience working with lead-sheathed wiring? The streetlights in my area (built 1939-1940) are fed by the original lead-covered wire in UG steel conduit.
It's low-voltage (240v) lighting.

In most areas the old stuff is holding up fine, but there are a couple of spots with recurrent problems. The City wants to replace all the conduit and wire with new. Cost for the rewiring is expected to run $675k.

So, I have a few questions:

1. What's the construction of the wire? I'm assuming copper conductor with rubber insulation and lead sheathing; would anything else have been used around 1940?

2. How long can such wiring be expected to serve reliably? I've heard of medium-voltage UG feeders sheathed with lead that are working fine after over 100 years.

3. Is this kind of wire prone to becoming stuck in the conduit? If so, do you have any info on the effectiveness of chemicals used to free wire in conduit (I know Coke can be used to good effect, if it's dried soap-based lube causing the problem). Any experience with a situation like this?

4. Any experience megging out this kind of underground wiring? What sort of resistence values indicate good wiring? I know that if it gets to that point, it'd be a question of using a meg-ohm meter to find the weakest links; but if anyone has experience with this, it'd be great to hear it.

I'm an electrical contractor and volunteer consultant just looking into options; the City staff seem pretty determined to tear out the old, even though the maintenance logs don't show widespread or frequent problems. And I'd rather not see public money spent unless it's necessary.

Thanks in advance--

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Re: Lead-insulated conductors [Re: SactoCliff] #195474 08/05/10 12:17 AM
Joined: Jul 2002
Posts: 8,397
Trumpy Offline
Member
Hi there Cliff,
I have quite a bit of experience with Lead Sheathed cables.
Back when I started my time as an apprentice Liney here in New Zealand we were taking out this sort of cable (mainly singles) used to feed the odd commercial building.

To be honest, lead is something that everyone is against because of it's effect on the environment.
Sure, the cable might be OK, but at the end of the day, it really does need to be replaced with something "safer".

The actual cable itself uses a jute weave insulation upon a copper inner conductor, hence, if it gets wet at all, you can expect either a fault to earth which will often blow out a large section of the lead insulation and damage the jute insulation.

The reason we started replacing these cables was because of the clamps used to earth the outer sheath, would work loose over time, in so much that they became a safety risk with fuses not clearing when they should have done.

Lead is a very soft metal and very hard to keep a really good clamping force on, without deforming the sheath (which also reduces the insulation resistance at that point).

Mate, IMO, either XLPE or PVC sheathed cables HAVE to be better than Lead sheathed cables.
In a place where it was not possible to replace the Lead cables, I was sent to joint one, one night.
All I can say is it was a real nuisance, it took 4 and a half hours to joint a cable that should have taken an hour at the most.

Cliff,
Times change, as far as I can see $675K would be a small price to pay for peace of mind.
I never want to see another lead sheathed cable again, they've had their day, let's move on.

Re: Lead-insulated conductors [Re: Trumpy] #195485 08/05/10 06:22 PM
Joined: Jun 2004
Posts: 1,273
T
Tesla Offline
Member
Use until failure is a poor notion for most City circuits.

At least the raceway should be plenty wide for THWN-2 or equivalent.


Tesla
Re: Lead-insulated conductors [Re: Tesla] #195497 08/06/10 10:24 AM
Joined: May 2005
Posts: 984
G
ghost307 Offline
Member
I still see a fair amount of existing lead cables and most people are too cheap to automatically replace them.
My standard answer to "can we splice into the existing lead wiring and re-use it?" is as follows:

"It is indeed possible to splice old lead cables, but it's also possible to drill a hole in a potato chip. I'll give you an alternate price for replacing them so that we're covered both ways".

In my experience, as soon as you touch them there's a gigantic probability that they will fail.


Ghost307
Re: Lead-insulated conductors [Re: ghost307] #195503 08/06/10 05:41 PM
Joined: Aug 2009
Posts: 13
SactoCliff Offline OP
Member
Excellent information; thank you all.

And Tesla, I'm thinking along the same lines; it'd be great to use the existing raceway, if possible. There's a lot of sidwalk, driveway, lawn, and plantings to tear up if they run new conduit.

On the other hand, I'd expect that the original lead-sheathed conductors were pulled in with soap as a lubricant, and could be pretty well stuck.

Thanks again,

Cliff


Re: Lead-insulated conductors [Re: SactoCliff] #195520 08/08/10 04:19 PM
Joined: Apr 2003
Posts: 362
Obsaleet Offline
Member
I have seen this maney times to post lights and things the problem may be that depending on the size of conduit the that wire may be corroded in place, in the conduit. I have gotten some to come out but some of the lead sheath stayed behind. LOL Others come free no problem. I pretty much consider this an ungrounded system. The lead outer jacket is not very good for grounding. Almost all the systems I have found this stuff on were ungrounded.


Choose your customers, don't let them choose you.
Re: Lead-insulated conductors [Re: Obsaleet] #195536 08/09/10 08:03 PM
Joined: Apr 2005
Posts: 48
U
uksparx Offline
Member
I have dealt with a lot of lead sheathed cables in homes in the UK. It was used extensively until the advent of rubber sheathed and pvc sheathed came along. As you guys have all said, it is a pig to ground properly, you have to have skill and patience to ensure a good connection. Even then, with time they loosen and become ineffective - best to get rid I say, yup, they have had their day.
We do still have a lot of underground lead sheathed service cables though, the same grounding issues arise here. Only recently I had to check out the grounding on someone's home and found it totally useless due to a crack in the service cable lead sheath. The Utility company arrived PDQ when I pointed out this!


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