200 Amp PVC to RMC Transition in Crawlspace

[G_Gordon]

Hi All,

I have a 400 Amp Service and Meter on a pedestal about 150' from our house (it's located here because it's equidistant between the house and a barn).

The plan is to service the house with 200 amps in 3/0 stranded copper. Currently, we have 3" PVC Schedule 40 entering the house below grade through the concrete foundation wall. At the inside of the foundation wall, this transitions to a a 3" PVC LB Conduit Body.

My idea is to locate the 200 Amp subpanel for the house directly above this conduit body, on the main floor of the house, which will make it a ~6' vertical run. I am inclined (maybe even required?) to make this vertical run with 3" RMC.

I think this question has been asked in the forum a few times, but it doesn't seem to be settled.


My questions are:

At what points should I make the RMC transition to the PVC, and using what adapter(s)?

Where should I utilize the threaded end of the RMC, and with what adapter(s)?

What is the most secure way to connect the RMC to the subpanel and support the RMC from its weight bearing down on the PVC Conduit Body?

This is my own house, and we are installing some of the conduit and having our electrician pull the wire and hook up the feeders.

 

[G_Gordon]

And to complicate matters slightly, it appears the largest knockout on the 200 Amp QO Load Center is 2.5"...

 

[petersonra]

We do not answer diy questions here.

Since you are going to have an electrician involved, I suggest you ask him


Personally, I have no idea why you would want to make this transition at all.

 

[G_Gordon]

First of all, this isn't a DIY question. We run our own conduit all the time in order to coordinate and optimize framing penetrations. Forum rules say the site is for "Contractors", among others.

Second, there are a variety of opinions on how to best make these transitions, which is why I am bringing it up on the forum. Isn't that what the forum is for?

Third, the transition to RMC is important because the 200amp feeders will be far more protected in the wall cavity (subject to nails, screws, etc) than in PVC.

 

[petersonra]

Three inch conduit seems plenty big to run three 3/0 wires and a #6 egc. It would probably work with inch and a half, certainly two inch.

If you are worried about the size of the knockouts drop the size down to 2-1/2.

You did say in your op that it was your own house.

In any case, it seems best to have your electrician answer these questions for you since he will have to deal with whatever you end up doing.

 

[winnie]

The reason that we do not answer DIY questions is because we have no idea what you do not know outside of the specific question you are asking. It is assumed that a professional electrician knows the bulk of the code, but is stumped on a particular issue, whereas a non-electrician will ask about a particular issue, not knowing what they don't know about the rest of the installation.

The moderators will be the final arbiters of what is allowed, but in general they permit non-electricians to ask questions to help better specify jobs that an electrician will be doing.

In the OPs case, the first question to ask: are the conductors in question 'service conductors', meaning are they unfused conductors coming from the utility? The OP calls the 200A panel a 'subpanel', but it is being fed from a 400A meter pedestal, and might actually be wired as a service panel.

If these are service conductors, not protected by an upstream breaker, then there are much stricter requirements then if these are feeder conductors with upstream protection. If these are service conductors then the distance inside the house will be restricted, and the length limit inside the house are vary widely depending upon the interpretation of the permitting authority. IMHO if these are service conductors you will want to keep these conductors _outside_ of the house as much as possible.

If these are feeder conductors, then PVC conduit will be perfectly code acceptable inside the wall of the house. If your personal preference is to have the greater protection of RMC, then you are welcome to use it. You might also consider keeping the conduit as PVC for the entire run, and then using some sort of metal sleeve around the conduit to protect it in the wall.

The transition from PVC to RMC can be done with a PVC threaded adapter. I personally would use a metallic LB and make the transition from underground PVC to RMC. You might also consider using a much larger 'pull box', with PVC entering the pull box and then RMC leaving the box. Your electrician can size this box, but because of that 3" conduit it will be big. (Something like 18" square or larger.)

For the wires size being considered, you don't need 3" PVC. I assume that this larger size conduit was selected to make an easier pull, or for future expansion capacity. Inside the house, where 3" PVC won't fit the breaker panel and won't fit in the wall, you should probable transition to a smaller conduit. The wire size being considered would fit in 2" PVC, and (depending upon ground and neutral size) might even fit some types of nominal 1.5" conduit.

Make sure that you consider issues of slope and drainage for your underground conduit run, otherwise it can be a great path for water to enter your house.

-Jon

 

[petersonra]

He is going to need a disconnect out at the meter.

 

[G_Gordon]

Jon,

Thank you for the thoughtful reply.

The reason that we do not answer DIY questions is because we have no idea what you do not know outside of the specific question you are asking. It is assumed that a professional electrician knows the bulk of the code, but is stumped on a particular issue, whereas a non-electrician will ask about a particular issue, not knowing what they don't know about the rest of the installation.

We are very familiar running conduit and pipe. We are less familiar with the latest best practices for transitions between dissimilar materials. In this case, RMC and UL Schedule 40 PVC.

The moderators will be the final arbiters of what is allowed, but in general they permit non-electricians to ask questions to help better specify jobs that an electrician will be doing.

Agreed, and much appreciated.

In the OPs case, the first question to ask: are the conductors in question 'service conductors', meaning are they unfused conductors coming from the utility? The OP calls the 200A panel a 'subpanel', but it is being fed from a 400A meter pedestal, and might actually be wired as a service panel.

These are service conductors protected by an upstream 200A breaker at the pedestal. (The barn is likewise protected by its own 200A breaker.)

If these are service conductors, not protected by an upstream breaker, then there are much stricter requirements then if these are feeder conductors with upstream protection. If these are service conductors then the distance inside the house will be restricted, and the length limit inside the house are vary widely depending upon the interpretation of the permitting authority. IMHO if these are service conductors you will want to keep these conductors _outside_ of the house as much as possible.

If these are feeder conductors, then PVC conduit will be perfectly code acceptable inside the wall of the house. If your personal preference is to have the greater protection of RMC, then you are welcome to use it. You might also consider keeping the conduit as PVC for the entire run, and then using some sort of metal sleeve around the conduit to protect it in the wall.

It is our preference to have RMC, but the metal sleeve is definitely a nice consideration if the inspector will allow it.

The transition from PVC to RMC can be done with a PVC threaded adapter. I personally would use a metallic LB and make the transition from underground PVC to RMC. You might also consider using a much larger 'pull box', with PVC entering the pull box and then RMC leaving the box. Your electrician can size this box, but because of that 3" conduit it will be big. (Something like 18" square or larger.)

So a basic PVC Female Threaded Adapter is the way to go? That's easy enough.

I think the pull box will be cumbersome and problematic because we have several other conduits entering the house at the same location.

The transition to a metal LB at this location is a nice idea but it is a pretty tight fit to get a wrench behind the LB in this location, making the glued PVC connection rather preferable. (We also like the PVC Conduit Body so that in the event we do get some water entering the conduit and flooding back towards the house, it wont pool in the bottom of a steel conduit body. (we're in favor of weep holes in locations like this if the inspector sees the logic; ours does)

For the wires size being considered, you don't need 3" PVC. I assume that this larger size conduit was selected to make an easier pull, or for future expansion capacity.

Yes, to make the pull easier.

Inside the house, where 3" PVC won't fit the breaker panel and won't fit in the wall, you should probable transition to a smaller conduit. The wire size being considered would fit in 2" PVC, and (depending upon ground and neutral size) might even fit some types of nominal 1.5" conduit.

I think we will reduce to 2" right above the conduit body.

Make sure that you consider issues of slope and drainage for your underground conduit run, otherwise it can be a great path for water to enter your house.

Agreed.

-Jon

Thank you, Jon!

 

[G_Gordon]

He is going to need a disconnect out at the meter.

There is a service disconnect at the meter.

 

[G_Gordon]

Three inch conduit seems plenty big to run three 3/0 wires and a #6 egc. It would probably work with inch and a half, certainly two inch.

This was just to make the pull easier.

If you are worried about the size of the knockouts drop the size down to 2-1/2.

Yes, I think we will step down to 2" after the LB.

You did say in your op that it was your own house.

Yes, sometimes contractors even get to build their own houses. (and yes, they are usually, so-called, "overkill")

In any case, it seems best to have your electrician answer these questions for you since he will have to deal with whatever you end up doing.

Sometimes we like to "engineer" and coordinate our runs more than the average electrician, and think before making penetrations in the framing, for example. Again, it's my house, and we are fortunate we have the time to take the necessary steps to plan things out and make equipment runs neat and clean and get the details right.

 

[winnie]

Sometimes we like to "engineer" and coordinate our runs more than the average electrician, and think before making penetrations in the framing, for example. Again, it's my house, and we are fortunate we have the time to take the necessary steps to plan things out and make equipment runs neat and clean and get the details right.

As someone who sometimes wears the "engineer" had, an important caution is to not over-specify a job. Your role as customer and contractor should be to specify the desired outcome, and then let the particular trade involved specify the specific way to achieve that end.

Since you are in a position to coordinate runs, you can say 'electrical service gets this space claim, CATV gets this claim, water gets this....'. Your goal is to have neatly routed and easy to understand utilities, coordinated across the trades. So it makes good sense to specify the different trade's space claims.

Why specify an oversized conduit run? What is your goal? If you are doing the pull, in a sense acting as a sub for the electrician, then I agree it makes sense to specify a conduit run which you are happy to use. But if the electrician is doing the pull, what is _your_ goal? If your only goal is to have the conductors end up connected, then you should let the electrician decide on conduit size. If your goal is an easy pull to permit future repairs, then focus your specification on that requirement. The EC will almost certainly have the best approach given local conditions (and supply house availability) to achieve your desired end goal. For example it might be better to use a smaller diameter run of continuous HDPE conduit rather than larger pieced together PVC.

If you are specifying a larger than necessary conduit because you don't trust your EC to select a combination of conduit, lube, pulling tools, etc. to obtain a good result, then you might need to re-think your EC!

IMHO it makes more sense for you to specify the location of the breaker panel and the requirement that the interior run be protected by metal then to specify the portion of the run be in RMC with a particular transition.

Sorry, off my soapbox now. Any craftsperson knows the difference between doing the bare minimum and doing something _well_, and it sounds like you are aiming for 'done well'. It is just easy to overspecify a tiny part of the job and end up with something that meets that specification but doesn't actually achieve your goals.

-Jon

 

[ggunn]

These are service conductors protected by an upstream 200A breaker at the pedestal. (The barn is likewise protected by its own 200A breaker.)

If they are protected by an OCPD they are not service conductors. It's a feeder.

 

[electrofelon]

There is a service disconnect at the meter.

1. I would use 230.40 exception number 3 and not have a disconnect at the meter. Then you could only run three wires and not have the extra equipment at the meter.
2. I would not transition to RMC.
3. I would probably reduce down to a two and a half inch lb and then go up into the panel with that.
4. Not sure if it was mentioned, but to use the forum you have to be an electrician or involved with the electrical trade specifically, not just a contractor. I am not a moderator so it's not my call but I'm sure one will step in here soon.

 

[G_Gordon]

Wow, okay.

As someone who sometimes wears the "engineer" had, an important caution is to not over-specify a job. Your role as customer and contractor should be to specify the desired outcome, and then let the particular trade involved specify the specific way to achieve that end.

As an architect and builder we typically like to discuss both desired outcomes AND how we this will be achieved. Some trades simply don't understand the philosophy or goals of a particular project.

For the purposes of average American residential projects, you're right, but this project is a little different.

Since you are in a position to coordinate runs, you can say 'electrical service gets this space claim, CATV gets this claim, water gets this....'. Your goal is to have neatly routed and easy to understand utilities, coordinated across the trades. So it makes good sense to specify the different trade's space claims.

Yes, we coordinate this with the trades. But in this project, we're not turning them loose with a spade bid and a roll of pex tubing and saying "have fun".

Why specify an oversized conduit run?

The electrician specified the conduit run.

What is your goal?

According to him, to make the long pull easier.

If you are doing the pull, in a sense acting as a sub for the electrician, then I agree it makes sense to specify a conduit run which you are happy to use. But if the electrician is doing the pull, what is _your_ goal?

See above.

If your only goal is to have the conductors end up connected, then you should let the electrician decide on conduit size.

He did, see above.

If your goal is an easy pull to permit future repairs, then focus your specification on that requirement. The EC will almost certainly have the best approach given local conditions (and supply house availability) to achieve your desired end goal. For example it might be better to use a smaller diameter run of continuous HDPE conduit rather than larger pieced together PVC.

I realize I haven't provided pictures, but as I mentioned, it's a very straightforward short run and for safety reasons we want RMC. I prefer less plastic than more especially in the living space.

If you are specifying a larger than necessary conduit because you don't trust your EC to select a combination of conduit, lube, pulling tools, etc. to obtain a good result, then you might need to re-think your EC!

Asked and answered. See above.

IMHO it makes more sense for you to specify the location of the breaker panel and the requirement that the interior run be protected by metal then to specify the portion of the run be in RMC with a particular transition.

My question is whether there is a preferred transition from one conduit type to another in a particular, straightforward application. I could ask anyone. My EC, the building inspector, or I could post a question on this forum and ideally inspire a few different answers coming from different angles and we might all learn something... this is, perhaps, the strength of a community of people collaborating on a forum.

Sorry, off my soapbox now. Any craftsperson knows the difference between doing the bare minimum and doing something _well_, and it sounds like you are aiming for 'done well'. It is just easy to overspecify a tiny part of the job and end up with something that meets that specification but doesn't actually achieve your goals

You and I might have different ideas about what it means to overspecify something. For me, I don't think this is one of those situations. It's easier for us to make some pretty basic conduit runs (less than 10') and have the EC come out when when it's time to pull. Yes, I could call him and he would probably stop by, or he could come to do the install and realize he doesn't have a part, and has to come back, etc. etc. ad nauseam, but at 6am I thought someone from this forum might have a friendly suggestion.

-Jon

Cheers!

 

[G_Gordon]

1. I would use 230.40 exception number 3 and not have a disconnect at the meter. Then you could only run three wires and not have the extra equipment at the meter.
2. I would not transition to RMC.

Because today is Tuesday, or is there a rationale you'd like to share?

3. I would probably reduce down to a two and a half inch lb and then go up into the panel with that.
4. Not sure if it was mentioned, but to use the forum you have to be an electrician or involved with the electrical trade specifically, not just a contractor. I am not a moderator so it's not my call but I'm sure one will step in here soon.

Good grief. I've made it clear I'm a contractor. This is a legitimate question (and debated elsewhere on the forum) about the methods for joining two dissimilar conduit types in a particular application. I'm not asking how to wire a light switch.

 

[electrofelon]

Because today is Tuesday, or is there a rationale you'd like to share?

Good grief. I've made it clear I'm a contractor. This is a legitimate question (and debated elsewhere on the forum) about the methods for joining two dissimilar conduit types in a particular application. I'm not asking how to wire a light switch.
View attachment 2567297

Regarding 230.40 exception number 3, the advantage is you don't need a disconnect at the meter which is more equipment more cost and more terminations, and then you only need to run three wire instead of four wire to the structures.

Regarding the transition to RGS, if you really want to go ahead and do it, I would just think 99% of electricians would not do that. Believe me, I understand going top shelf on your own house. In my house I installed a true commercial panel board instead of a load center. You can transition using a female adapter or in your case I would probably use a metallic threaded lb and transition at the lb . Assuming you don't have threading equipment, you would need to get a threadless connector for the rigid on one end. Note you would need to assure the rigid conduit is bonded.

 

[G_Gordon]

Regarding 230.40 exception number 3, the advantage is you don't need a disconnect at the meter which is more equipment more cost and more terminations, and then you only need to run three wire instead of four wire to the structures.

Understood. My EC already installed the meter disconnect. I seem to recall something about it being required because of the PV system, but I could be wrong.

Regarding the transition to RGS, if you really want to go ahead and do it, I would just think 99% of electricians would not do that. Believe me, I understand going top shelf on your own house. In my house I installed a true commercial panel board instead of a load center. You can transition using a female adapter or in your case I would probably use a metallic threaded lb and transition at the lb . Assuming you don't have threading equipment, you would need to get a threadless connector for the rigid on one end. Note you would need to assure the rigid conduit is bonded.

Thank you for this, exactly the type of feedback I was looking for. Greatly appreciated.

 

[don_resqcapt19]

if you are on the 2020 or 2023 code cycle, you will need an outside emergency disconnect at the house.

 

[ggunn]

if you are on the 2020 or 2023 code cycle, you will need an outside emergency disconnect at the house.

See post #12.

 

[eds]

I believe a disconnect will be required on the exterior of the house, unless the interior panel is close to the location of the feeder entrance. Use a reducer in the 3'' pvc female adapter. Utilize EMT instead of rigid. Why 3/0 copper, and not 250 alu?