Adding liquidtight to rigid metal conduit

[BlueBaron]

Hello I have an existing run of rigid metal conduit outside of my house that feeds several outdoor receptacles. There is no separate ground wire inside the rigid metal conduit. Is there a way that I can use liquid tight to run to a new extension receptacle? What I am particularly concerned about is how to make sure that I have the grounding right. There is no existing ground wire within the rigid metal conduit. Thank you

 

[James]

Flexible conduit is not suitable for use as an earth.

you need to draw an earth cable down the rigid conduit
or
use a box to join rigid to flexible, you can then use the box to connect an earth lead for the flexible conduit to carry.

 

[BlueBaron]

Flexible conduit is not suitable for use as an earth.

you need to draw an earth cable down the rigid conduit
or
use a box to join rigid to flexible, you can then use the box to connect an earth lead for the flexible conduit to carry.

Thank you so much, I won’t be able to draw a ground wire down the rigid conduit at this point. However if I understand your other solution, I can add a metal junction box to the rigid metal conduit. Then run a ground wire from that junction box to my receptacle. Does that make sense? Thank you

 

[James]

Yes, you have managed to decrypt my poorly worded description perfectly

 

[BlueBaron]

Thank you so very much!!!!

 

[James]

Obviously you need to confirm that the rigid conduit has a good bond to earth itself, if it is not earthed then the whole thing is a possible danger.

 

[BlueBaron]

Obviously you need to confirm that the rigid conduit has a good bond to earth itself, if it is not earthed then the whole thing is a possible danger.

Good point. I think it is but it was installed so long ago, I am not sure. What do you think about driving a grounding rod into the ground and then connecting the grounding rod to the rigid conduit? I would do that just to be extra careful that it was grounded some how.

 

[James]

Not sure on the requirements n the USA,
@Megawatt is a well respected USA member who may know a bit more on that point.
in the U.K., I would test to see what the resistance between main earth and the conduit was and make decision based on the results.

 

[Megawatt]

Not sure on the requirements n the USA,
@Megawatt is a well respected USA member who may know a bit more on that point.
in the U.K., I would test to see what the resistance between main earth and the conduit was and make decision based on the results.

Is the conduit installed all the way to the panel, if so then the metal conduit can be your ground. From there as stated above you will then install a metal junction box, then you can pull a ground wire from the box and then you can install flex to your receptacles. Don’t install a ground rod for a grounding electrode. If the conduit doesn’t go all the way to the panel then pull a ground wire through the conduit and if you have metal water piping then ground it. Then fish a wire from your panel and through the wall to go down to under your house and ground the conduit. If you do that then you have created a grounding electrode for your panel. Good luck

 

[BlueBaron]

Is the conduit installed all the way to the panel, if so then the metal conduit can be your ground. From there as stated above you will then install a metal junction box, then you can pull a ground wire from the box and then you can install flex to your receptacles. Don’t install a ground rod for a grounding electrode. If the conduit doesn’t go all the way to the panel then pull a ground wire through the conduit and if you have metal water piping then ground it. Then fish a wire from your panel and through the wall to go down to under your house and ground the conduit. If you do that then you have created a grounding electrode for your panel. Good luck

Thank you so much! This is super helpful. The conduit appears to run uninterrupted all the way to the panel, but I cant see the whole run. Is there a way to use a multimeter or something else to test that it runs uninterrupted all the way to the panel? Thanks so much!!

 

[pc1966]

Thank you so much! This is super helpful. The conduit appears to run uninterrupted all the way to the panel, but I cant see the whole run. Is there a way to use a multimeter or something else to test that it runs uninterrupted all the way to the panel? Thanks so much!!

Yes, at least in the UK you can get a "wander lead" that is typically 50m (around 164 feet) that allows you to measure resistance with a suitable meter. Here are some examples:

R2 Wander Lead Suppliers | Low Prices

www.tester.co.uk

I presume the same is available in the USA, or you just get a reel of flexible wire and some crocodile clips.

Incidentally they are called "R2" leads here as when electricians talk of the cable resistances during testing R1 is the hot/line/live and R2 is the ground/earth/CPC. Typically they are used for exactly the sort of job you are seeing, but usually for a ground wire rather than conduit (same electrical purpose in both cases).

Usually for such a measurement you would use a low resistance meter that is design for the job, typically here in the UK they are part of insulation resistance testers (typically testing at 250V/500V/1000V DC) or a "multi function tester".

The main difference compared to a multimeter is they go down to around 0.01 ohm, and they usually have a 'null' button to allow you to zero the reading with the test cable(s) connected together so you then measure just the equipment being checked. Also they are usually safe if something was accidentally energised, as that can lead to a very bad day indeed!

TL;DR Get enough wire, measure its resistance, connect to your conduit and panel, measure result and subtract. If small enough then they are joined!

 

[pc1966]

Thank you so much! This is super helpful. The conduit appears to run uninterrupted all the way to the panel, but I cant see the whole run. Is there a way to use a multimeter or something else to test that it runs uninterrupted all the way to the panel? Thanks so much!!

The other way, and typically how we would do it, is you disconnect hot wire at the panel and connect it to the earth bar. Then at the far end you measure hot-ground and that gives you R1+R2

We would combine that reading with the supply impedance and then check enough current would flow so the breaker would disconnect under fault conditions fast enough (typically under 0.4s).

 

[pc1966]

I should also add that if you are working with mains electricity you really should make sure your multimeter is rated at CAT-III or CAT-IV so if you make a mistake with the settings it won't explode in your face.

That is no joke, under fault conditions an enormous amount of energy can be released, enough to cause 3rd degree burns, blindness, or even death (just search for "arc flash"). Adequately rated meters are designed not to fail badly under the different electrical conditions possible (over voltage and prospective fault current).

Here is what I mean by CAT-III etc

Measurement category - Wikipedia

en.wikipedia.org

Here are examples of meters to consider, but check the details:

14 Best Multimeters in 2024 - Review by an Electrical Engineer

In this article, Electrical Engineer Chris Schiebel, reviews some of his favorite DMMs in a one-stop-shop buying guide to multimeters.

www.betterhomeguides.com

Something at $34 or so to consider:

https://www.digikey.com/en/products/detail/klein-tools-inc/MM300/6597021

 

[pc1966]

Having looked at the Klein meter's specifications you might want to consider the MM400 as it adds AC current, or even as far at the MM700 at $111 as it gives you low R measurement.

However, AC current using a multimeter should be restricted to low power items, as typically the switch on surge will blow a safe meter's fuse. An electrician would typically use a clamp ammeter for general work as they are more convenient (no need to disconnect the cables) and safe to pretty high peak currents. For example:

https://www.digikey.com/en/products/detail/klein-tools-inc/CL120/12702195

 

[Megawatt]

Thank you so much! This is super helpful. The conduit appears to run uninterrupted all the way to the panel, but I cant see the whole run. Is there a way to use a multimeter or something else to test that it runs uninterrupted all the way to the panel? Thanks so much!!

Open up the panel and see if the conduit is in the panel with a lock nut to tighten it down