I've laid the wrong underground cable. Problems?

[carlyai]

I layed a 30 m section of power cable to the shed in conduit and buried it a couple of feet deep underground.

Previously I laid THW-A 1 x 25mm2 750 V overhead, and then NYY 1 x 25mm2 underground.

Just looking at some past threads and realised NYY is only copper and what I put down was Al and the THW-A instead.

I also put it in 2 inch yellow conduit not the black stuff.

Am i going to have to rip it up and put down the NYY?

[Crossy]

THW (copper) and THW-A (aluminium) are not intended for use under ground (specifically excluded on the Bangkok Cable page).

In reality, if it's protected by an RCD / RCBO at the supply end and you can keep the wet out then it will last a few years.

What's in the shed if it needs 25mm² cable?

I'm assuming this is an internal installation and not being connected to an MEA/PEA meter (who won't connect to Al underground).

[carlyai]

I had the THW and NYY cables left over from running the house cable.

I just grabbed the wrong cable. Looking at them today I don't realise how you could make such a mistake. ?

The shed is not directly fed from the PEA.

I have an outside consumer unit feeding the shed through a 32A breaker at the consumer unit and a RCD in the CU at garage.

I'll have to replace the 32A breaker with a RCD.

I used wire that was left over and the shed will use a bit of arc welding, hydrophonics, and irrigation system and pump (but ain't got that far yet).

Edited March 26, 2016 by carlyai

[williet98248]

30 meters is a long distance but if you have laid it in a 2 inch conduit can't you attach the proper cable to the end and pull it through (fish it though)? Of course if you have bends in the conduit it will be difficult. But if a straight pipe you would only have to dig a pit at both ends to get a straight pull. Worth some thought anyway.

[bark]

If you don't know anything about Electric or building, why are you even trying, Save 100 bt , cost you 10,000.

[steven100]

attach the correct cable onto the wrong one and pull it through .... no need to dig it up ....

[orpheus454]

THW (copper) and THW-A (aluminium) are not intended for use under ground (specifically excluded on the Bangkok Cable page).

Is that right? I thought THW (copper) was OK in conduit underground but NYY was OK bare.

[carlyai]

30 meters is a long distance but if you have laid it in a 2 inch conduit can't you attach the proper cable to the end and pull it through (fish it though)? Of course if you have bends in the conduit it will be difficult. But if a straight pipe you would only have to dig a pit at both ends to get a straight pull. Worth some thought anyway.

[carlyai]

Hi Williet. I have thought about that and it is a solution.

What i did yesterday is compare the two types of cable, and did some www reading. (will try to upload some pics from my drop box).

The THW-A and the NYY are similar looking end on, difference being the NYY has two outer sheeths of insulation where the THW only has one.

AND one is Cu and the other Al.

As the cable has been installed in thick 2 inch conduit and buried a couple of feet deep, I don't think it is going to be hit when gardening.

If water gets in the conduit it has to seap through 1 layer of insulation where as with the NYY it has to seap through 2 layers of insulation. How long will it take water to seap through 1 layer?

Any idiot can see that the NYY is Cu and not Al, but not this idiot.

Both Cu and Al oxidise. On reading about underground Al cables, It seems that there is a problem with them if there is a join. I don't have a join.

So weighing this all up, and knowing that you never run THW underground, and that in 10 years I'll be 81 years old, I'm going to leave the cable there and see what fails first, the cable or me.

[carlyai]

If you don't know anything about Electric or building, why are you even trying, Save 100 bt , cost you 10,000.

[carlyai]

It's not about the money bark, it is about having a go.

So I was pretty stupid.

Edited March 28, 2016 by carlyai

[carlyai]

attach the correct cable onto the wrong one and pull it through .... no need to dig it up ....

[carlyai]

Thanks for the reply steven, I have though about that, after the embarrasment of my stupidity attach.

[steven100]

Thanks for the reply steven, I have though about that, after the embarrasment of my stupidity attach.

That's fine, anyone can make a mistake like that .... you'll get it resolved ... plan first.

[Crossy]

THW (copper) and THW-A (aluminium) are not intended for use under ground (specifically excluded on the Bangkok Cable page).

Is that right? I thought THW (copper) was OK in conduit underground but NYY was OK bare.

http://www.bangkokcable.com/product/backoffice/file_upload/131004_1-450!750V%2070C%2060227%20IEC%2001%20%28THW%29.pdf

Look in the Applications box, last entry.

[carlyai]

Attached are pix of cable comparison and conduit used.

[Crossy]

A post has been removed.

This forum is no place for racist remarks.

[williet98248]

Hi Williet. I have thought about that and it is a solution.

What i did yesterday is compare the two types of cable, and did some www reading. (will try to upload some pics from my drop box).

The THW-A and the NYY are similar looking end on, difference being the NYY has two outer sheeths of insulation where the THW only has one.

AND one is Cu and the other Al.

As the cable has been installed in thick 2 inch conduit and buried a couple of feet deep, I don't think it is going to be hit when gardening.

If water gets in the conduit it has to seap through 1 layer of insulation where as with the NYY it has to seap through 2 layers of insulation. How long will it take water to seap through 1 layer?

Any idiot can see that the NYY is Cu and not Al, but not this idiot.

Both Cu and Al oxidise. On reading about underground Al cables, It seems that there is a problem with them if there is a join. I don't have a join.

So weighing this all up, and knowing that you never run THW underground, and that in 10 years I'll be 81 years old, I'm going to leave the cable there and see what fails first, the cable or me.

Probably what I would do as well. At 74 years I too am thinking about how long I am going to last compared to other things in my life. Family history tells me I have 10-15 years left.

[carlyai]

Hi Williet. There must be a very good reason they say not to lay this type of cable underground, but I'm not sure if the main reason is that it's easily damaged or the water can seap through to the centre conductor. It's already been in the ground one wet season. Crossy commented that it could last a bit.

There i was so proud at having dug a good trench and installed the cable with the help of the Mrs, and I've put the wrong frigging cable in, when i knew it should have been NYY. Beats me!

I'm digging another trench now to run cable to another bore pump, and it will be NYY.

[sometimewoodworker]

Hi Williet. There must be a very good reason they say not to lay this type of cable underground, but I'm not sure if the main reason is that it's easily damaged or the water can seap through to the centre conductor. It's already been in the ground one wet season. Crossy commented that it could last a bit.

There i was so proud at having dug a good trench and installed the cable with the help of the Mrs, and I've put the wrong frigging cable in, when i knew it should have been NYY. Beats me!

I'm digging another trench now to run cable to another bore pump, and it will be NYY.

Having seen your example of the conduit the cable is in, assuming that the underground section is installed the usual way, it probably won't be waterproof as the joints are usually a push fit with no solvent.

An alternative, probably cheaper too, would be to use LDPE/ HDPE pipe as that is sold in 50 or 100 meter lengths. Of course that does not guarantee that it won't get punctured and so leak, but it does start off as watertight.

[carlyai]

Hi Williet. There must be a very good reason they say not to lay this type of cable underground, but I'm not sure if the main reason is that it's easily damaged or the water can seap through to the centre conductor. It's already been in the ground one wet season. Crossy commented that it could last a bit.

There i was so proud at having dug a good trench and installed the cable with the help of the Mrs, and I've put the wrong frigging cable in, when i knew it should have been NYY. Beats me!

I'm digging another trench now to run cable to another bore pump, and it will be NYY.

Having seen your example of the conduit the cable is in, assuming that the underground section is installed the usual way, it probably won't be waterproof as the joints are usually a push fit with no solvent.

An alternative, probably cheaper too, would be to use LDPE/ HDPE pipe as that is sold in 50 or 100 meter lengths. Of course that does not guarantee that it won't get punctured and so leak, but it does start off as watertight.

[carlyai]

So it seems my main problem is water in the conduit.

Does this mean the water will seap through the insulation to the centre conductor as the conduit joints are just pushed together?

If that is so, why can't it do the same with the NYY cable, but take longer?

[sometimewoodworker]

So it seems my main problem is water in the conduit.

Does this mean the water will seap through the insulation to the centre conductor as the conduit joints are just pushed together?

If that is so, why can't it do the same with the NYY cable, but take longer?

Sorry you really need someone like Crossy to give you the reasons and problems with burying the wrong cable in the wrong conduit, if there are any.

All I know, from asking too many questions to the PEA supervisor friend of SWMBO who oversaw our temporary meter install, is that the LDPE/HDPE pipe was a recommendation, that he would not connect to an AL cable unless it was overhead, that copper, overhead, underground in conduit or not was the other option with single or double insulation.

I did not as enough the find the limits of single insulated copper, but suspect that it can't be buried without an outer protection.

We have just had copper installed in LDPE clipped to a wall I will check it out later to see if it is single or double insulated.

FWIW the PEA uses double insulated cable overhead.

[carlyai]

So it seems my main problem is water in the conduit.

Does this mean the water will seap through the insulation to the centre conductor as the conduit joints are just pushed together?

If that is so, why can't it do the same with the NYY cable, but take longer?

Sorry you really need someone like Crossy to give you the reasons and problems with burying the wrong cable in the wrong conduit, if there are any.

All I know, from asking too many questions to the PEA supervisor friend of SWMBO who oversaw our temporary meter install, is that the LDPE/HDPE pipe was a recommendation, that he would not connect to an AL cable unless it was overhead, that copper, overhead, underground in conduit or not was the other option with single or double insulation.

I did not as enough the find the limits of single insulated copper, but suspect that it can't be buried without an outer protection.

We have just had copper installed in LDPE clipped to a wall I will check it out later to see if it is single or double insulated.

FWIW the PEA uses double insulated cable overhead.

[carlyai]

Thanks for that.

I'll have to put on my list of things to do to replace the cable and conduit.

There is a reason the cable manufacturers give precautions.

In saying that both the AVR manufacturer and water heater manufacturer said i couldn't connect my 3 phase incoming to 3 single phase AVR's and 3 single phases to 3 phase instant water heaters, and they've been working fine for a while now.

[steven100]

Thanks for the reply steven, I have though about that, after the embarrasment of my stupidity attach.

don't worry , you'll get it corrected and fixed , if I was nearby I would come and help.

it's just a simple mistake ..... it'll turn out ok .....

[carlyai]

Looking at some other sites, from other western countries, THW cable has a good insulation resistance and the W indicates 'water resistant' and can be layed in wet or dry conditions.

So are the Thai cable manufacturers being over cautious in their ratings (always best to be), or is their W water proof rating not as good as other countries W rating?

Edited March 29, 2016 by carlyai

[carlyai]

So it seems my main problem is water in the conduit.

Does this mean the water will seap through the insulation to the centre conductor as the conduit joints are just pushed together?

If that is so, why can't it do the same with the NYY cable, but take longer?

Sorry you really need someone like Crossy to give you the reasons and problems with burying the wrong cable in the wrong conduit, if there are any.

All I know, from asking too many questions to the PEA supervisor friend of SWMBO who oversaw our temporary meter install, is that the LDPE/HDPE pipe was a recommendation, that he would not connect to an AL cable unless it was overhead, that copper, overhead, underground in conduit or not was the other option with single or double insulation.

I did not as enough the find the limits of single insulated copper, but suspect that it can't be buried without an outer protection.

We have just had copper installed in LDPE clipped to a wall I will check it out later to see if it is single or double insulated.

FWIW the PEA uses double insulated cable overhead.

[carlyai]

I'm digging another trench from my shed to the irrigation pump.

I bought some 6m2 nyy 3 conductor and the black with red strip conduit to house the cable in.

The conduit is not very flexible so how did you go about going from an in ground horizontal run, to out of ground vertical run? Did you use sand in the pipe and heat it, or is it flexible enough to bend a radius?

I bought some snakes heads to connect to the shed and pump wiring.

Eventually i'll connect to a submersible pump, but at the moment I'm trying to check the dynamic water level in my bore with an above ground pump.