EMT questions

[rmack898]

I'm planning the electrical install on my new shop. I will be using surface mounted EMT and have a question. When joining EMT to boxes, Ell's, and unions, what is the preferred method? Set screw couplings or compression couplings?

From a strictly aesthetics point of view, I think the compression joints look so much better. How do they compare to other methods of ground current conductors?

 

[alfredeneuman]

I'm planning the electrical install on my new shop. I will be using surface mounted EMT and have a question. When joining EMT to boxes, Ell's, and unions, what is the preferred method? Set screw couplings or compression couplings?

From a strictly aesthetics point of view, I think the compression joints look so much better. How do they compare to other methods of ground current conductors?

Set screw and compression fittings are equal in their grounding ability.
Use whichever you please.
Properly installed EMT is a better grounding conductor than a copper ground wire.

 

[rmack898]

Thanks Al,
I guess I'l be using compression fittings for all my joints.

 

[Bert_]

Set screw is much faster. For either type I much prefer steel over die cast.

 

[acer66]

Properly installed EMT is a better grounding conductor than a copper ground wire.

Why is that?

 

[Bert_]

Why is that?

A lot more metal in even a 1/2 emt compared to a #12 wire.

 

[acer66]

A lot more metal in even a 1/2 emt compared to a #12 wire.

Makes sense, are there any pitfalls besides loose screws/nuts
and maybe not enought overlap at joints?

 

[Terry D]

I'm my own opinion, always run a equipment ground.

Sent from my SM-G960U using The Garage Journal mobile app

 

[sberry]

It's something about the pipe surrounding the wire I think.

 

[Max]

I’m a EE, not a sparky. But my understanding is that NEC allows using the EMT as the ground. Steel is a worse conductor than copper, but there is so much steel in comparison to 12 AWG wire that in the end the resistivity of the steel EMT is much less than the copper wire.

Having said the above, for the EMT I put in my shop I included a ground wire in the EMT. I agree with Terry, and the reason I added the ground was that in the future, if any of the connections got loose (for example, someone screwing with the EMT) I still wanted to have a ground through all of the boxes, outlets, and EMT segments. Kind of a belt and suspenders approach, and maybe the sparkies would consider it a waste of money, but for me it’s cheap insurance decades down the line. The last thing I ever want to have is EMT that is energized...

Max

 

[Norcal]

I’m a EE, not a sparky. But my understanding is that NEC allows using the EMT as the ground. Steel is a worse conductor than copper, but there is so much steel in comparison to 12 AWG wire that in the end the resistivity of the steel EMT is much less than the copper wire.

Having said the above, for the EMT I put in my shop I included a ground wire in the EMT. I agree with Terry, and the reason I added the ground was that in the future, if any of the connections got loose (for example, someone screwing with the EMT) I still wanted to have a ground through all of the boxes, outlets, and EMT segments. Kind of a belt and suspenders approach, and maybe the sparkies would consider it a waste of money, but for me it’s cheap insurance decades down the line. The last thing I ever want to have is EMT that is energized...

Max

If the grounding conductor was not bonded at the connection points, having the additional grounding conductor makes things worse.

 

[Max]

If the grounding conductor was not bonded at the connection points, having the additional grounding conductor makes things worse.

I am kind of scratching my head trying to figure out how this could be worse. In one case you have a missing ground due to an issue in the EMT connections somewhere, and in the other case you have the same fault that may or may not be covered by the ground wire. So how can the ground wire make it worse? I can see where the ground wire would not help, but worse escapes me...

In my case it’s moot - the ground wire is connected to each box, outlet, etc. So the EMT would have to have two bad connections for there to be an issue.

- Max

 

[BigGarage]

I am kind of scratching my head trying to figure out how this could be worse. In one case you have a missing ground due to an issue in the EMT connections somewhere, and in the other case you have the same fault that may or may not be covered by the ground wire. So how can the ground wire make it worse? I can see where the ground wire would not help, but worse escapes me...

In my case it’s moot - the ground wire is connected to each box, outlet, etc. So the EMT would have to have two bad connections for there to be an issue.

- Max

I'd also like to understand how it be "worse". I used EMT all along the walls of my garage and all of the metal boxes have the outlets grounded to them.

Dennis

 

[Norcal]

I'd also like to understand how it be "worse". I used EMT all along the walls of my garage and all of the metal boxes have the outlets grounded to them.

Dennis

If you connected the grounding conductor to the box, it is good, it's when you don't is what my comment was about.

 

[grounded-b]

I am kind of scratching my head trying to figure out how this could be worse. In one case you have a missing ground due to an issue in the EMT connections somewhere, and in the other case you have the same fault that may or may not be covered by the ground wire. So how can the ground wire make it worse? I can see where the ground wire would not help, but worse escapes me...
- Max

Having a grounding conductor surrounded by a non-grounded, ferrous tube, creates a "choke". In the case of high fault current on the grounded conductor, during a short circuit, the inductance caused by the choke, causes very high impedance on an AC circuit.

High impedance limits the current flowing back to the source. Breakers may not trip.

Steve

 

[aka Larry]

From a strictly aesthetics point of view, I think the compression joints look so much better. How do they compare to other methods of ground current conductors?

The set screws look like absolute **** IMO, so used the compression fittings in my shop as well.

I know the EMT can be used as the ground, but I ran a ground wire just for overkill.

 

[BigGarage]

If the grounding conductor was not bonded at the connection points, having the additional grounding conductor makes things worse.

I'd also like to understand how it be "worse". I used EMT all along the walls of my garage and all of the metal boxes have the outlets grounded to them.

Dennis

If you connected the grounding conductor to the box, it is good, it's when you don't is what my comment was about.

Thank you. I guess I'm good to go. I used the set-screws and don't mind them at all, hell, it's a garage.

Dennis

 

[Norcal]

Thank you. I guess I'm good to go. I used the set-screws and don't mind them at all, hell, it's a garage.

Dennis

But you used those effing handy boxes which means the wire fill volume was exceeded there is almost never a good reason to use them.

 

[BigGarage]

But you used those effing handy boxes which means the wire fill volume was exceeded there is almost never a good reason to use them.

I don't know what this means. Please explain.

Dennis

 

[Bert_]

I don't know what this means. Please explain.

Dennis

Handy boxes and those plastic covers are a sure sign of a diy. It's not wrong, except wire fill can be an issue, but no pro would do it that way. 4x4 boxes and raised covers is the way to go. Probably end up cheaper than the handy boxes too. 4x4 boxes and covers are cheap because they are so common in the industry.

 

[exranger06]

All boxes have a specific volume of space inside. Every wire and device (outlet, switch, etc) takes up space in the box. You cannot exceed the volume of the box. For example, a #12 wire uses 2.25 cubic inches of space. If you have 5 #12 wires in the box, you're using 12.25 cu in. If the box has a capacity that's less than 12.25 cu in, it's a code violation. I don't know what the cu in volume of handy boxes are, but I'm guessing Norcal has an idea and knows you're probably over the limit.

One violation I noticed is that your conduit isn't secured. EMT is required to be strapped at least every 10 ft, and within 3 ft of boxes/terminations.

 

[Max]

Having a grounding conductor surrounded by a non-grounded, ferrous tube, creates a "choke". In the case of high fault current on the grounded conductor, during a short circuit, the inductance caused by the choke, causes very high impedance on an AC circuit.

High impedance limits the current flowing back to the source. Breakers may not trip.

Steve

I understand chokes and inductance. I am skeptical that a length of EMT (say 10’) could create a choke of high enough inductance that it could limit hundreds of amps at 60 Hz. Is this something that you have seen yourself?

Also, please remember that we got into this situation because the EMT connection to ground was broken somewhere along the path. So in the case of no ground wire and using the EMT for ground, in this situation with the “broken EMT” the breaker will not trip anyway.

I am not trying to argue, or to “win”, but who knows who will look at this information in a web search down the line and so I’d like to be as correct as we can.

I think that the bottom line is that the NEC allows the use of the EMT itself as the grounding conductor, and that the NEC also does not prohibit adding a ground wire when using EMT. So either option is to code.

Max

 

[slackjaw]

Handy boxes and those plastic covers are a sure sign of a diy. It's not wrong, except wire fill can be an issue, but no pro would do it that way. 4x4 boxes and raised covers is the way to go. Probably end up cheaper than the handy boxes too. 4x4 boxes and covers are cheap because they are so common in the industry.

It's also worth calling out that with a plastic cover, you have to run a ground from the outlet to the box. If you use a metal cover and a self-grounding outlet (common), you don't need to run that wire, as the outlet is grounded via the cover/screws.

 

[slackjaw]

Handy boxes and those plastic covers are a sure sign of a diy. It's not wrong, except wire fill can be an issue, but no pro would do it that way. 4x4 boxes and raised covers is the way to go. Probably end up cheaper than the handy boxes too. 4x4 boxes and covers are cheap because they are so common in the industry.

The set screws look like absolute **** IMO, so used the compression fittings in my shop as well.

I know the EMT can be used as the ground, but I ran a ground wire just for overkill.

Totally agree. I always run compression. You have to use a wrench to ensure you get a tight fit that won't come apart, but compression looks so much cleaner. There have been studies showing that EMT compression and set-screws survive Earthquakes, so the idea that it might just come apart in the future isn't something you need to worry about unless you don't have confidence in your ability to screw or wrench something tight.

 

[Terry D]

Its just common practice to install a equipment ground in my area. You pigatail it to the box, and each receptacle and/or switches. And then continues to the next box. The only time I personally come across a installation with not a equipment ground, is something that was installed years ago.

 

[Terry D]

It's also worth calling out that with a plastic cover, you have to run a ground from the outlet to the box. If you use a metal cover and a self-grounding outlet (common), you don't need to run that wire, as the outlet is grounded via the cover/screws.

Totally agree. handy boxes should be outlawed

 

[That Guy Scott]

I don't know what this means. Please explain.

Dennis

http://electricalslang.com/Slang/handy box

He means these

 

[dscheidt]

All boxes have a specific volume of space inside. Every wire and device (outlet, switch, etc) takes up space in the box. You cannot exceed the volume of the box. For example, a #12 wire uses 2.25 cubic inches of space. If you have 5 #12 wires in the box, you're using 12.25 cu in. If the box has a capacity that's less than 12.25 cu in, it's a code violation. I don't know what the cu in volume of handy boxes are, but I'm guessing Norcal has an idea and knows you're probably over the limit.

One violation I noticed is that your conduit isn't secured. EMT is required to be strapped at least every 10 ft, and within 3 ft of boxes/terminations.

Common handy box is 13 cubic inches. Four 12 AWG wires connected to a device require 13.5 cubic inches, so not legal, even worse if you're running a separate ground, or have wires just passing through the box. They're very little cheaper to use than a 4" square box, so there's little reason to use them except in the rare case where there's really not room for a bigger box. (The boxes cost more around here than a plain 1900 box, but the cover is cheaper than an exposed work cover. )

while I agree that compression fittings look a little better than set screw ones, I spend zero time looking at them in my shop spaces. Badly bent conduit, on the other hand....

 

[dscheidt]

It's also worth calling out that with a plastic cover, you have to run a ground from the outlet to the box. If you use a metal cover and a self-grounding outlet (common), you don't need to run that wire, as the outlet is grounded via the cover/screws.

You don't. Handy boxes have built in ears for mounting the device to, so the device is properly grounded (assuming it's a self grounding type, of course), even with no cover at all. A metal cover, if fitted, is grounded by the mounting screw(s) to the device body.

 

[wyliesdiesels]

I prefer compression fittings. Looks cleaner IMHO

It's also worth calling out that with a plastic cover, you have to run a ground from the outlet to the box. If you use a metal cover and a self-grounding outlet (common), you don't need to run that wire, as the outlet is grounded via the cover/screws.

Actually the device is grounded via its yoke which is bonded to the metal box by the screws.

The faceplate has nothing to do with it

 

[Norcal]

Totally agree. handy boxes should be outlawed

My attitude with those boxes is, if you want to use them put your finger on a anvil, & have someone hit each finger 10 times with a 5# hammer, after that if still want to use them, then go for it. A 4 sq box and a raised cover is a better choice almost every time.

 

[BigGarage]

All boxes have a specific volume of space inside. Every wire and device (outlet, switch, etc) takes up space in the box. You cannot exceed the volume of the box. For example, a #12 wire uses 2.25 cubic inches of space. If you have 5 #12 wires in the box, you're using 12.25 cu in. If the box has a capacity that's less than 12.25 cu in, it's a code violation. I don't know what the cu in volume of handy boxes are, but I'm guessing Norcal has an idea and knows you're probably over the limit.

One violation I noticed is that your conduit isn't secured. EMT is required to be strapped at least every 10 ft, and within 3 ft of boxes/terminations.

I have 14 gauge wire and the conduits were all firmly secured after I finished painting the wall. I secured even more often than required by code, almost always do.

Dennis

 

[BigGarage]

It's also worth calling out that with a plastic cover, you have to run a ground from the outlet to the box. If you use a metal cover and a self-grounding outlet (common), you don't need to run that wire, as the outlet is grounded via the cover/screws.

I don't know if you are referencing my pics but if you are then my other post clearly states that every outlet is grounded to the metal box it is in.

EDIT: They are all grounded to the metal boxes with a separate ground wire from outlet to box.

Dennis

 

[BigGarage]

Common handy box is 13 cubic inches. Four 12 AWG wires connected to a device require 13.5 cubic inches, so not legal, even worse if you're running a separate ground, or have wires just passing through the box.

I just brought in a handy box from the bunch I have out in the garage and the inside specs are 3 3/4"x 2"x 1 3/4". This gives 13 1/8 cubic inches. I used 14 gauge wire so unless there's something wrong with that I guess I'm OK.

It's kind of hard to believe that it would violate code to connect an outlet in an outlet box using 14 gauge wire.

Dennis

 

[BigGarage]

Handy boxes and those plastic covers are a sure sign of a diy. It's not wrong, except wire fill can be an issue, but no pro would do it that way. 4x4 boxes and raised covers is the way to go. Probably end up cheaper than the handy boxes too. 4x4 boxes and covers are cheap because they are so common in the industry.

Well I am a do-it-yourselfer. I have shelves full of electrical stuff including many plastic outlet & switch covers. I wasn't about to let them sit there while I bought 25 metal ones.

4x4 boxes may have been better to some people but I wanted to space the outlets every 30" along the wall. I was not going to wire up a 4x4 box every 30". Just my preference.

Dennis

 

[BigGarage]

http://electricalslang.com/Slang/handy box

He means these

Thank you.

Dennis

 

[sberry]

Like anything else hand have their place. It's up to the installer to know where to use them. Not every switch or end run recept needs a 4x4 in case a guy wants to tie a nuke plant in the end of one.

 

[Bert_]

I just brought in a handy box from the bunch I have out in the garage and the inside specs are 3 3/4"x 2"x 1 3/4". This gives 13 1/8 cubic inches. I used 14 gauge wire so unless there's something wrong with that I guess I'm OK.

It's kind of hard to believe that it would violate code to connect an outlet in an outlet box using 14 gauge wire.

Dennis

General rule of thumb is the handy boxes are only good for the last outlet in a run or a switch loop. Basically room for one set of wires and a switch or outlet. Running in and out of the box plus the device will often be over fill.

 

[Milton Shaw]

One thing that is available now that was not 50 years ago is offset EMT fittings that allow EMT to be flush with the wall without having to do a double bend. Now they have a bender that will do the double bend that lets the EMT line up with the box and yet be tight against the wall. I remember all the struggles I had in getting the right offset and keeping both bends and then the bend at the top of the wall headed in the right direction. Either way you need the EMT offset fittings or the offset bender to do a neat job. Also make sure you remove the burs inside the pipe from whatever method you cut the pipe. The small M12 porta Band does a quick job of getting the pipe the right length without excessive burs like a pipe or tubing cutter does.

 

[sberry]

Got then for 50 cents a piece a bit ago.
I was in an old guys shop a while back, really good mechanic but plumber by trade and a true old master that learned as he went and over the time got a real grip on supply and demand. He has a 5 hp 2 stage comp he installed 50 years ago with some 1/2 steel line and still uses it today. They know with some exceptions the code is the size to use for normal ****. Any hose he has will get the water out fast enough for what we are doing. He understands making it better but also has a grip on the fact the 16 cord works just fine.
I have installed hundreds of handi probably but they at the end of a pipe most of the time for convenience but if I had to look back at how much greif installing them has cost me its zilch and in the end if it were to happen as simple as unbolting a box. I cant think of a time right now, hundreds of installs and I cant think of once or twice in a career its been an issue, same for most of this future proofing. Most upgrades been obsoleted, energy savings, more hydrants but in most case less demands, more cheaper tools with a little less peak demand but more of them.
We now drill, cut and grind at 2 amps vs 12 of old via the cordless tool. Have a fist full of batteries and 4 drills running screws on a roof would have taken a couple cords in days of olds. Now done at a slower rate via a charger. Same for water fixtures, now 1.6 flush max and some a lot lower. Doesn't even scald a guy out with a flush anymore.