Electrical cable - Buried in a trench - checking on steps and rules

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timbosan

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#318326 7-Jan-2025 13:55

Hi all, this is somewhat of a followup to another thread (I am not the OP) https://www.geekzone.co.nz/forums.asp?topicid=280420

I have dug a trench, 600mm deep, between the house and retaining wall, and will do the same on the other side of the wall and come up just outside a cabin I built. I have 2 runs of 32mm orange conduit, one for power (will be 6mm TPS) and the other for data (I already have an outdoor rated Cat6 cable that is strung to the cabin, this will go into the second conduit).

I also have the electrical warning tape, but I cannot find a copy of AS/NZ 3000:2018 without having to pay a large sum of money, so checking on Geekzone if I have done everything correct :-)

Trench is 600mm from ground level
2 separate conduits for power and data
Backfill to 300mm then lay warning tape
Add in warning signs at both end of the trench
Conduits will exit inside a wall (I am lucky enough that the exit point is an area I am rebuilding, including a nib wall and new framing, due to recent repealing work)

Anything I have missed? Some photos for reference:

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#3328718 7-Jan-2025 15:32

1st off although not significant we use AS/NZS3000:2007 (2018 not yet cited in NZ)

Is the conduit medium or heavy duty? - if it's medium duty you will need additional mechanical protection.

Do you have an inspector lined up? a electrician cannot certify homeowner work.

You will need 50mm of bedding material above and below the conduit (sand)

MikeFly

148 posts

Master Geek

#3328812 7-Jan-2025 18:34

Nice job of the trench Timbosan. Having recently done the same its hard yakka, esp considering I have a bloody digger but couldn't get it into where I needed the trench.

Daynger

435 posts

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#3328813 7-Jan-2025 18:35

gregmcc:

1st off although not significant we use AS/NZS3000:2007 (2018 not yet cited in NZ)

Is the conduit medium or heavy duty? - if it's medium duty you will need additional mechanical protection.

Do you have an inspector lined up? a electrician cannot certify homeowner work.

You will need 50mm of bedding material above and below the conduit (sand)

Indeed, we, qualified electricians and inspectors use NZS3000:2007 and the amendments, he, being a homeowner should be using ECP51 and getting any work inspected and connected by an inspector.

ECP51 is freely downloadable.

SomeoneSomewhere

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#3328818 7-Jan-2025 18:53

Only need sand/friable soil if it's bare cable in the trench (SWA/NS). Conduit can be buried in any soil except large rocks.

Needs to be a 50mm gap between the two conduits, but this is the least enforced rule out there.

Shouldn't use orange conduit for data. AS/NZS3000 suggests white. Remember you need warning tape at half depth, and glue the joints. Above ground conduit should be white for UV stability.

I don't remember if ECP51 includes provision for underground? If not, you will need to work closely with your electrician for the full length of the project. They will essentially have to sign off that you were performing the work under their supervision. This is not something they should do lightly.

mdooher

Hmm, what to write...
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#3328822 7-Jan-2025 18:58

Why would it need to be in bedding if it is in a wiring enclosure?

Matthew

gregmcc

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#3328827 7-Jan-2025 19:15

SomeoneSomewhere:

Only need sand/friable soil if it's bare cable in the trench (SWA/NS). Conduit can be buried in any soil except large rocks.

need to figure out if it's a CAT A or CAT B protection, if it's medium duty conduit it's CAT B which requires bedding. I'm guessing the OP doesn't know if it's heavy duty or not.

SomeoneSomewhere:

I don't remember if ECP51 includes provision for underground? If not, you will need to work closely with your electrician for the full length of the project. They will essentially have to sign off that you were performing the work under their supervision. This is not something they should do lightly.

ECP51, pg 20 has the requirements for underground cables.

Electricians CANNOT sign off homeowner work - only a inspector can, As far as an electrician supervising a homeowner doing electrical work, I doubt that is withing the scope of what supervision covers, it either needs to be as a homeowner which included that it must be checked by an inspector, or it's done under supervision which requires agreement and a trainee limited certificate.

timbosan

2159 posts

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#3328837 7-Jan-2025 19:26

MikeFly:

Nice job of the trench Timbosan. Having recently done the same its hard yakka, esp considering I have a bloody digger but couldn't get it into where I needed the trench.

LOL, thanks! Yeah I thought "I can do this in a day" and then struck an old brick path and the concrete base of a washing line, several major roots from trees, and now it's already day 4. But MOST of the trench is done to 600mm, so I can at least start to backfill the completed parts.

Samsung

Shop now on Samsung phones, tablets, TVs and more (affiliate link).

timbosan

2159 posts

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#3328838 7-Jan-2025 19:27

Daynger:

gregmcc:

1st off although not significant we use AS/NZS3000:2007 (2018 not yet cited in NZ)

Is the conduit medium or heavy duty? - if it's medium duty you will need additional mechanical protection.

Do you have an inspector lined up? a electrician cannot certify homeowner work.

You will need 50mm of bedding material above and below the conduit (sand)

Indeed, we, qualified electricians and inspectors use NZS3000:2007 and the amendments, he, being a homeowner should be using ECP51 and getting any work inspected and connected by an inspector.

ECP51 is freely downloadable.

I have an inspector handy, so all covered there. They are a sparky + inspector and he will be doing the panel + wiring in the cabin.

timbosan

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#3328840 7-Jan-2025 19:33

SomeoneSomewhere:

Only need sand/friable soil if it's bare cable in the trench (SWA/NS). Conduit can be buried in any soil except large rocks.

Needs to be a 50mm gap between the two conduits, but this is the least enforced rule out there.

Shouldn't use orange conduit for data. AS/NZS3000 suggests white. Remember you need warning tape at half depth, and glue the joints. Above ground conduit should be white for UV stability.

A few questions @SomeoneSomewhere :

Orange vs. white - is this a regulation or something that makes identification easier if ever dug up?

Warning tape - already have that sorted, will be laid at 300mm fill.

Gluing joints - this is something I am not sure of. The other thread I linked to had the comment below:

"You can not bother to glue the joints at all, or you can glue the joints with great care. If the conduit is PERFECTLY waterproof, it will still fill with water, as moist air will enter and moisture will condense, and stay in the conduit. All outside conduits are defined as wet locations, and all cables in them must be wet rated, or failures will be expected."

I took this as it doesn't really affect the water tightness due to moisture in the air. I do have the sealant stuff for plumbing, happy to be corrected on if this is needed.

And thanks :-)

timbosan

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#3328843 7-Jan-2025 19:35

gregmcc:

need to figure out if it's a CAT A or CAT B protection, if it's medium duty conduit it's CAT B which requires bedding. I'm guessing the OP doesn't know if it's heavy duty or not.

I checked, its all here https://www.mitre10.co.nz/shop/marley-arma-rigid-conduit-32mm-x-4m-orange/p/333806

CAT A underground
Heavy duty 4431

SomeoneSomewhere

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#3328863 7-Jan-2025 19:59

Cat A or B only require soft fill if they're cables not in an enclosure. 3.11.4.2. I do need to admit a mea culpa; underground the separation between power and comms is 100mm.

I don't really want to go digging through the regs and act again, but the sections that allow trainees to do work supervised all have a section next to them that allow anyone to do work supervised, just with stricter restrictions on the work that can be done. It's irrelevant as it's an Inspector involved anyway.

I don't think 3000 has any control over your data wiring other than it being a distance away. Nothing prohibits orange, but if it ever gets dug up, colour coding is better. Green would be nice but you can't easily get green that's not marked as Chorus.

Gluing helps prevent it coming apart due to movement while backfilling, or later subsidence. Agreed that it won't help with waterproofing.

neb

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#3328880 7-Jan-2025 21:03

timbosan: I have 2 runs of 32mm orange conduit, one for power (will be 6mm TPS) and the other for data (I already have an outdoor rated Cat6 cable that is strung to the cabin, this will go into the second conduit).

Anything I have missed?

I wouldn't have a long run of Cat6 run in parallel to mains cable, and even without that issue would be nervous about electrically connecting two buildings or whatever with ethernet. Better to run fibre and put a media converter on each end, or an SFP into a switch/router if you're using one.

SomeoneSomewhere

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#3328882 7-Jan-2025 21:09

The parallel routing is only a data/link integrity concern, and shouldn't be significant given it looks like a relatively short run.

If it's a 2C+E submain then there shouldn't be any significant concerns with voltage difference. If it's a 2C 'outbuilding' system with an earth stake and MEN link in the outbuilding, you will get some ground bounce and shouldn't be running conductive services in parallel. It shouldn't be an issue with ethernet given the galvanic isolation, but it's not good practice or compliant.

If there's a nearby lightning strike, all bets are off either way.

timbosan

2159 posts

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#3328976 8-Jan-2025 07:58

neb:

timbosan: I have 2 runs of 32mm orange conduit, one for power (will be 6mm TPS) and the other for data (I already have an outdoor rated Cat6 cable that is strung to the cabin, this will go into the second conduit).

Anything I have missed?

I wouldn't have a long run of Cat6 run in parallel to mains cable, and even without that issue would be nervous about electrically connecting two buildings or whatever with ethernet. Better to run fibre and put a media converter on each end, or an SFP into a switch/router if you're using one.

Interesting comment, I actually looked at running fibre as I thought "10gig speeds!" but realised my switches are only 1gb. But its a good idea, I have SFP ports available and just need the cable.

timbosan

2159 posts

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#3328978 8-Jan-2025 08:11

SomeoneSomewhere:

The parallel routing is only a data/link integrity concern, and shouldn't be significant given it looks like a relatively short run.

If it's a 2C+E submain then there shouldn't be any significant concerns with voltage difference. If it's a 2C 'outbuilding' system with an earth stake and MEN link in the outbuilding, you will get some ground bounce and shouldn't be running conductive services in parallel. It shouldn't be an issue with ethernet given the galvanic isolation, but it's not good practice or compliant.

If there's a nearby lightning strike, all bets are off either way.

From what I understand it's a submain - the quote notes:

- RCbo in the main switchboard
- Miniture switchboard in the cabin with 2 x RCBOs

The total distance of the conduit will be under 8 meters.

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