Steel wired armoured cable in the garden

[gocsan]

Hello

I have an existing steel wired armoured cable in my garden that was previously connected to my old garage that is already dismantled. The SWA cable was buried directly into the ground without any conduit. Due to some tree removals and ground excavation, I've had to dig up the cable and will need to bury it again. I'm planning to re-use this cable to power a light and a double socket to a shed that I haven't built yet. I'm in the middle of renovating my garden, so I'm planning to do as much prep work as possible on my own before I hire an electrician to install the light and socket when the shed is ready. So the only thing I'll be doing is bury the cable into the ground and have the end point of the cable next to my new shed or inside it.

I have a couple of questions:

- Is it a legal requirement to have the SWA cable in a conduit before burying it into the ground? Or can I just bury the SWA cable as it is into the ground like how the previous owner had done it? I don't want to bury it without conduit only for the hired electrician to reject the light/socket installation due to this issue. I don't want to lift the cable back up after having paving slabs installed around the shed.

- Is there some legal requirement as how deep I need to bury the cable?

I appreciate your responses.

 

[Andy™]

SWA is suitable for direct burial, no duct required (although it can be fitted)

Deep enough to avoid damage. general guidelines would be 450mm but can vary

 

[Lurch]

Is it a legal requirement to have the SWA cable in a conduit before burying it into the ground?

No.

Is there some legal requirement as how deep I need to bury the cable?

No.

You can use some speaker wire buried with no conduit if you want, legally. I think you may be getting "to the current regulations" and "legally" mixed up.

SWA is direct burial and doesn't need any additional mechanical protection. Depth is as deep as it needs to be. If it is under slabs or a path then it doesn't need to be ridiculously deep, under a flower bed and it would be wise to bury it fairly deep. General gist is between 450mm & 1m depending on where it is exactly and how likely it is to be caught/damaged.

As for the "I will do everything then get the electrician to come round" thing, you should get them to pop their head in now before it is all buried and they say they can't use it for whatever reason, or they might want it doing a particular way.

 

[Tony S]

If the cable has been dug up then damage to the outer serving is likely. Damp and wire armourings equals rust, not what you want if the armour is used as the CPC.

 

[Doc Hudson]

Welcome to the forum. The first thing you need to do in my opinion before worrying about its method of installation, is to double check that the cable has not already been damaged by your excavations or by natural wear and tear from its original installation and or the conditions it is buried in. I would suggest you need to confirm the continuity of all the conductors and prove that the insulation is not damaged by doing an insulation resistance test between all conductors and the armour. These are very simple tests for an electrician with a suitable test meter. The best course of action would be to contact your local electrician ask them to come and verify the cable is all in good working order and whilst there, they can confirm that your proposed method of re-burying it will not present any dangers or hazards.

The legality aspect pivots around if you are expecting a formal certificate confirming that the work is safe and complies with BS7671. There are guidelines for all aspect of electrical installation work, but BS7671, (wiring regulations), is actually a non-statutory document that can have deviations providing that the person signing the certificate is confident it will not present any danger to people, property or livestock. As you say you don't want to do some work to then find either it is not acceptable or the cable has been damaged anyway so is unsafe.

As a rule of thumb any cable buried in ground that is likely to be re-dug in the future needs to be at least two spade depths deep (e.g. 450mm - 600mm min). If it is almost 99.9% certain it is never going to be re-dug and the route is clearly visible between the two points where it re-appears then a bit of discretion is possible. You need to take all reasonable steps to ensure that your cable is unlikely to be damaged during its lifespan by normal activities expected on that plot of land. Also you must take into consideration any compression effects on the cable from stones or sharp objects that could be increased due to surface traffic. e.g. any body who happens to bring in a mini digger or JCB is going to pull up almost anything you bury. A cable crossing a lawn or vegetable patch or a foot path down the side of a property, or a drive-way carrying cars in front of a house, are all very different beast even though the cable itself may only be buried for 3m length in each example.     

Doc H.  

 

[gocsan]

Welcome to the forum. The first thing you need to do in my opinion before worrying about its method of installation, is to double check that the cable has not already been damaged by your excavations or by natural wear and tear from its original installation and or the conditions it is buried in. I would suggest you need to confirm the continuity of all the conductors and prove that the insulation is not damaged by doing an insulation resistance test between all conductors and the armour. These are very simple tests for an electrician with a suitable test meter. The best course of action would be to contact your local electrician ask them to come and verify the cable is all in good working order and whilst there, they can confirm that your proposed method of re-burying it will not present any dangers or hazards.

The legality aspect pivots around if you are expecting a formal certificate confirming that the work is safe and complies with BS7671. There are guidelines for all aspect of electrical installation work, but BS7671, (wiring regulations), is actually a non-statutory document that can have deviations providing that the person signing the certificate is confident it will not present any danger to people, property or livestock. As you say you don't want to do some work to then find either it is not acceptable or the cable has been damaged anyway so is unsafe.

As a rule of thumb any cable buried in ground that is likely to be re-dug in the future needs to be at least two spade depths deep (e.g. 450mm - 600mm min). If it is almost 99.9% certain it is never going to be re-dug and the route is clearly visible between the two points where it re-appears then a bit of discretion is possible. You need to take all reasonable steps to ensure that your cable is unlikely to be damaged during its lifespan by normal activities expected on that plot of land. Also you must take into consideration any compression effects on the cable from stones or sharp objects that could be increased due to surface traffic. e.g. any body who happens to bring in a mini digger or JCB is going to pull up almost anything you bury. A cable crossing a lawn or vegetable patch or a foot path down the side of a property, or a drive-way carrying cars in front of a house, are all very different beast even though the cable itself may only be buried for 3m length in each example.     

Doc H.  

Many thanks for the detailed response. I guess I will get an electrician to inspect the cable first and then at the same time discuss further work with the light/socket installation when the shed is up.

Thanks for everyone else for your responses.

 

[gocsan]

I've just called up an electrician and one of the questions he asked was if this SWA cable is directly connected from the consumer unit. I guess I forgot to mention further details in regards to my current set up to you all. So I've explained to the electrician that the SWA cable is a single spur from a junction box (with an on/off switch) that is part of a ring main to my living room. Apparently he said that he would not be able to certify this shed work as any cabling to the garden would require a separate circuit breaker connection on its own directly to the consumer unit. Without a spare switch in my consumer unit, he said I'll have to upgrade my consumer unit with more circuit breaker slots and have a new cable connecting from the consumer unit to the shed. At this point I said I'll think about it.

Is there no way other way to do this other than go along with what the electrician said? I would imagine this is going to cost me quite a bit and wondering if it's worth having any electricity in my shed at all.

 

[Andy™]

find another electrician. ideally it should go back to the board but nothing wrong with being taken as a spur from a final circuit, seems like he wants to do more unnecessary work

 

[gocsan]

find another electrician. ideally it should go back to the board but nothing wrong with being taken as a spur from a final circuit, seems like he wants to do more unnecessary work

So the work that I originally want should be certifiable?

 

[ProDave]

Nobody has yet mentioned yellow "Elecrtrical cable below" warning tape to be buried above the SWA.

 

[Evans Electric]

I'd say you don't need a new consumer unit .

As said above , you need to know that the cable is'nt damaged anywhere .    Look for damage to the outer PVC sheath .

And if it is to be used , you need to to seal the end in the garden to stop damp seeping down the armouring .    Some electrical tape will do it. 

Your electrician would sort the rest out .

 

[Tony S]

I’d recommend a sheath test to be absolutely sure.

 

[Lurch]

So the work that I originally want should be certifiable?

Yes. I have 2 jobs to do next week, both doing exactly what you are asking for.