Steel Conduit as the CPC (Circuit Protective Conductor)

Can steel conduit be used as the CPC with no additional copper wire inside, and is it large enough for that purpose?
A look at the applicable regulations in BS7671, calculating the cross sectional area of steel conduit, and three ways to determine the size required.

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[XclubX]

JW is our conduit for useful information and a dry sense of humour which i definitely relate to

[sosurko]

Really good video. I have been investigating some points on an EICR. One point was the c2 given for no CPC conductor on a conduit system. The original install used the conduit. After carrying out continuity tests on the conduit system found it to be continuous. I tagged the boxes and carried out zs tests . No issues at all. Keep up the great videos

[getyerspn]

I have personally come across several installations that have ended up with no CPC continuity as the joints have either corroded or come loose or some one has hacked the install about and added extra hardware ..badly..I really don't like relying on the conduit as the CPC .. especially in industrial applications... Yes I know it's ok in the reg's .... But I always try to convince the customer to spend a bit extra for a separate CPC.
When the system is first installed using the Conduit as a CPC is ok but over time moisture and badly modified installations can cause the install to become dangerous... I've even found installs with what looked like pipe sealant on the threads with no CPC continuity at all.... I'm sure there are loads of others who've never seen these faults...but I have.

[mdy]

Practical, useful and short.
Thanks JW.

[XclubX]

1:07 JW has invented the multipurpose phone holder and selfie stick. . brilliant idea

[johnschlesinger]

I worked on a very large site in which about thirty sparks were installing conduit, trunking, and tray. A cpc was run through all conduits - just as well, as some of the sparks who were a bit slapdash would loosen off a conduit coupler if they hadn’t measured, bent and/or set the tube precisely. One slightly loose joint in a conduit system used as a cpc can, under earth fault conditions, cause a massive temperature rise, and start a fire, unless rcd protection is incorporated.

[muzikman]

It's essentially down to how good the original conduit install was as to wether it will maintain its integrity as a cpc. You are supposed to use galvanised paint on each joint to stop corrosion, but the reality is not many people do. If there is capacity to fit a separate cpc I would. It costs little more, and provides a more continuous and reliable cpc. Rusty joints, loose glands at accessories and poor quality workmanship = high resistance.. Just my opinion though. 😉 Great video JW

[KevinCoop]

John, I worked for electrical contractors for the last 35 years designing and managing. During that time, the owners of the companies all decided to not use conduit as "ground" (called here in US). They decided it was not worth the risk. People have died because the conduit came apart and became energized afterward. Yes it's legal here as well, just not necessarily a good practice. Respectfully, Kevin

[keithhowes]

Good point John and up until the late 1970s that is exactly what we did, but were this falls down is over time the couplers can corrode and give a very high resistance and in some cases I have seen the hole conduit rust through

[bostedtap]

Thanks for sharing and best regards from the Black Country.

[sengsothun]

Thank John for sharing this, I always want to know about using CPC on EMT.

[tinytonymaloney]

Wow, I have never worked this out, have always pulled an earth in because that's what's been spec'd. I couldn't believe how big the CSA of 20mm bar is but I worked out the size of a 20mm square bar which is 400mm sq. Then it made sense.
Good vid this JW but the sooth sayers will always want a cpc pulled onto the conduit, I don't think I have ever seen a conduit installation in the last 30 odd years without a CPC pulled in.

[daytonamann]

Hi John,

A great video as ever. I was wondering if you could do a video on using the armour of SWA as Cpc?

Regards

[UberAlphaSirus]

This is one of the regs I think are wrong, there are far to many weak links in the chain with contuit and truncking. corosion, bad joints, cutting grease left on, trunking caps bridging joints with not bond straps, etc. 5 odd years ago when I had an industril unit, the unit next door had a fault in thier conduit which had lost coninuity to the met and found an earth route via the roof suports to the emergency exit lighting thru all units and caused a fire because that conduit lost its met conection too but had a 1.5 cpc to earth for everything to dump to.

[allthegearnoidea]

Hello John. Very interesting and always and education. Do other metallic CMS such as box trunking or cable trays have the same allowance regarding not requiring a separate Earth ? I’m not an electrician, but I think the group standards I work to always specify a separate CPC. I see a lot of damaged conduit hanging off wall and think I would want a separate CPC in a conduit if I could. Regards Chris

[JimWhitaker]

Interesting. In another life I used to know something about "Tempest" precautions and testing. This related to the suppression/shielding of data signals in a secure environment. Steel conduit with screwed joints was demonstrated to be a very poor shield due (mainly) to high resistivity at the joints.

[SME_Ste]

On huge jobs where we use steel cable management, large amounts of money can be saved by using containment as the CPC.

Can imagine though in todays world the number of sparks stood there, scratching there heads thinking ‘oh no! Theres no earth installed’😩

[kevinramsay]

Hi John,
Top guy btw.
What would an electrician use to ensure continuity of a circuit that uses it's metal conduit as it's earth protection if the conduit was cut into to extend the circuit? I remember you mentioned that earth clamps must not be used.

[ashmanelectricalservices]

I personally would always endeavor to draw in a separate circuit protective conductor, I very much doubt a client is going have an issue paying for a separate circuit protective conductor, the installation time will be the same as the cpc can be drawn in at the same time as the line and neutral conductors.

[deemdoubleu]

Hi John, what about terminating steel conduit in a painted surface mount box of the type commonly used in garages etc. Would this require a 20 mm earthing tag fitted to the end of the conduit inside the box? i.e. in a similar fashion to SWA earth tag termination?