subelect

Replacing a 100 amp service, this afternoon installed the IMC service drop, meter-can with 100 amp breaker and RNC into the basement. Existing panel is 10 feet into the basement, across several joists. The plan on Monday is to attach an FA to the RNC, use Carflex (LTFNC) into the panel.

I have a couple of questions regarding this setup.
1. Because the meter-can has a disconnect, we are connecting the EGC from the ground rod to the neutral bar inside it. The new breaker box will be MLO. Doesn't the met-can become the Service Entrance? The reason that I ask is:
2. Now, the MLO brk box supply wires are not service conductors, but feeders. Or am I mistaken?
3. If that is a feeder, the restrictions of 230.43 to Steel Flex greater than 6 feet do not apply, do they? I am not a big fan of Carflex and would rather use Steel Flex.
4. If I use Steel Flex and attach it to the RNC FA, what is the easiest way to bond the Steel Flex? A bonding locknut or do I even need to bond that portion of the raceway if I am not using a concentric KO? If I use a bonding locknut, what section of 250 tells me what size AWG to have to use?
5. I will have to run a grounded conductor and an equipment grounding conductor from the met-can to the MLO bkr box. Do I use 250.122 or .66 to size the EGC?
Thanks,
Rick

kbsparky

This is essentially correct. Edit to add: Actually, it is your GEC, not the EGC that goes from the service neutral to the ground rod.

Bingo again.

You are on a roll here.

I believe this is also correct.

Your GEC sizing applies to the Service Equipment panel, which is outside with the meter. Table 250.66 applies to this.

250.122 is the table you need to use for equipment grounding conductor sizing. Both for your feeder cables and any bonding busings you care to utilize on the flex.

If you use listed fittings on the flex, and it is properly secured to the metal enclosure at least on one end, and you have included an EGC with your feeders, I don't believe you need any more than this in any case.

__________________
-KB

Life is uncertain -- eat dessert first!

subelect

Thank you, Rick

mikeg_05

How come you didn't use SER cable?

kbsparky

Why would anyone want to use that junk?

__________________
-KB

Life is uncertain -- eat dessert first!

mikeg_05

what is so wrong with it?

augie47

250.119 limits metal flex as your equipment ground to a 20 amp circuit. The IMC from the meter is bonded by it's connection to the meter. You need a seperate equipment grounding condutor in you conduit-flex run and there is no need for a bonding bushing or bonding locknut on the flex as it is not being used as part of the ground path.

subelect

Thanks for your input.
To the best of my knowledge, we have not used SER for several years. Every now and then we come across a house that has the service panel too far from the exterior; our AHJ says 5 feet is the max he will allow to meet the req. for keeping service wires as short as possible.

It was the crappy end to a really crappy week. The goal was to get the new service mast up and LB into the house before the weekend hit us with rain and lightning that would delay any of this work for next week.

Trying to find a good spot to install the met-can on the exterior wall, within the range of the existing 100 amp overhead service wires, staying 3' away from the window and over 10' off the backyard for the splices left me with only a few options. I had a different location several feet over picked out, but the boss said that he did not want to run very much RNC on the exterior surface of the house. So, I was kind of stuck with one location.

He is a good boss, but, like we used to say in the Navy, very "light lunch" regarding the NEC. The only guy he believes is the AHJ, which is not a bad thing, but it does kind of irk you that he has to hear it from him to believe you. I am not perfect by any stretch, but I try my best to keep up with the Code.

He had told me to call him to help lift up the met-can and service mast once I had gotten the RNC and LB installed.
I got the service wires and weatherhead installed while it was on the ground, then called him to hold it up while I attached it.
The bottom of the met-can is 3.5' off the ground; that keeps the splices 11' above finished grade and stays 3' from the window's moving parts.
He starts to tell me that there is a minimum height that the service entrance has to be and that I am below it.
I should have just shut up and let it go, but I was tired and being too much of a smart-...., I told him that only applies for a mobile home, not a permanent residence.
So, this puts us down the road of questioning every little thing.

Do I know if the city has an ordinance requiring specific height for their meters? (Out here in Podunk, USA??? The city utility has no req.)
How was I planning on getting across those 4 floor joist and above the sewage pipe? (Come out of the LB into an FA, steel flex into the panel.)
That is what brought up the question regarding length of service conductors in steel flex (not >6' per 250) and bonding the flex.

So, we put up the mast and met-can, after 3 different phone calls to the AHJ and city utility electricians. But I am sure he is going to ask me why I am running a #8 green with my 2-2-4 feeders to the MLO panel on Monday.
I wanted to ask you smart electricians to make sure that I have my facts straight in case he calls me on it.
Thanks again.
Rick

mikeg_05

hmm here its 15' max of unfused wire inside the house, which has to be in conduit. You said your meter can has a disconnect, so I was just curious why you did not use SER, we just did a new house with a 400 amp service, one panel in the garage, one downstairs, so we used a 200 amp disconnect for the panel downstairs. But it sounds like you got a good plan and figured it out

Peter D

Faster, cheaper, and relatively easy compared to pipe and wire.

kbsparky

Not so fast. In many installations where one uses a meter/main setup, there are provisions for branch circuits to originate from the service panel, which includes the meter in its assembly.

IF this is the case, then the sub-feed into the main house can be considered to have less than 100% of the dwelling's diversified load on it. This rules out the use of table 310.15(B)(6) when sizing your conductors.

This means that you can NOT use a #4/0 type SER cable when sub-feeding a 200 Amp panel. You have to upsize to a 300 kcmil, and that junk is not cheap, nor is it easy to install.

On a 100 Amp sub-feed, you have to utilize a minimum #1/0 SER under the same conditions.

The other problem I personally have with SER cable is the uninsulated grounding conductor tends to corrode over time in this area, where salt air conditions exist. We are close enough to the ocean here that sustained east winds bring salt-spray with it -- you can smell it -- and its effect on wiring systems is noticeable.

We use PVC conduit, and type THWN or XHHW conductors on most of our installations to avoid these problems.

__________________
-KB

Life is uncertain -- eat dessert first!