Combining the old with the new...

[dburoker]

I appreciate in advance the answers which I know will surely come. The resource provided to the public by all those who take the time to share their expertise certainly makes many DIYer's lives easier, safer, and of course, saves us all a bunch of money. Now on to my question:

I've built a detached workshop behind my house, and due to the need to budget and do things a step at a time, I did NOT get an electrical permit at the same time I got my building permit. That doesn't mean I won't get an electrical permit, it just means I needed to get the building shell completed, regroup (save up more $$), and then proceed. The building has been done for about a year, and the wife has given permission to now do the electrical and sheetrock work.

My house was built in 1970 and has the original meter, however the panel, switches, and receptacles were upgraded in 2007 when I bought the house. The local AHJ allowed the previous homeowner (their electrician) to replace the panel without upgrading the Service Entry cable, likely for the same reason I'll get to below- it is just about impossible to do without major destruction to my house. I'm OK with this, as I've inspected everything which currently exists and it is all in very good condition (existing meter base, service entry cable, newer panel). Yes, I have seen the inside of the meter box- it's in great shape, and the lugs are NOT rusty or corroded at all.

The meter base is just that- a meter base with no breakers. It's about 70' from the meter to the panel. I have 200A service.

So here's the deal:

My workshop is 10' behind the house, and it is 15' from the existing meter to the point which would be ideal to bring power into the shop. The newer panel is almost 100' from the workshop, so I'd really prefer for many reasons NOT to get power for the shop from the house panel. As I said before, the AHJ allowed the previous homeowner to retain the service entry cable, so I don't have separate neutral and ground between the meter and panel. The AHJ has also advised me that they will allow me to leave the service entry cable for the house as it is when I bring power into the shop.

Here's the big questions:

1.) Can I install a Main Lug Feed Through panel right under my existing meter, then rewire the existing service cable so that the service passes through the Feed Through Panel?

2.) I want to do this for budget and practical reasons. Everything works fine in my home. This was a doctors custom home back in 1970 and the original electrician did a good job. All my cable is copper, and all the circuits are very conservative. There is no #14 in the house, and every room has it's own breaker for receptacles, some have 2 or more. All lighting is on its own (several) circuits. It was done very well.

3.) If I can do the above mentioned MLO Feed Through panel, how would I best address the feeders between the new panel at the meter and the workshop? 3 wire, as with the old service conductors in the house... or 4 wire, like current code?

I know there will be a lot of opinions on this. I'm asking because my neighbor is a retired EE and he (for a hobby) has his Master Electrical license. He doesn't need the money. His solutions are based on the "most perfect method possible without regard to $$", and that is fine. I understand his position. I'm a Senior Network Engineer, and my solutions follow that same philosophy when practicable. On the other hand, I sometimes have to accept that perfection is not practical, and offer the best compromise. Because of this, I can't really get my neighbor to talk about anything other than perfection. Again, we are still friends, but I do prefer to be practical.

Current setup:
(Service from FPL)-----------(Meter)------ --------------------------------------(Panel in Garage)

Proposed setup:
(Service from FPL)-----------(Meter)------------(MLO Pass Thru)------------------(Panel in Garage)

60A CB
|
|
(Sub Panel in Workshop)​

The load calculations for the existing house put me at 127A. When I actually measure current with everything in the house turned on (and I mean oven, dryer, emergency heat, all lights, hairdryer, microwave, plenty of other stuff) I get between 105A and 112A. All looks good there. Load calculations for the workshop, which actually has an office space above it, are 58A. I'm well within the limits of my 200A service.

Thanks in advance.

 

[pattenp]

I think you need to run this by your AHJ. I think once you add the main lug panel even though if it is a feed through it changes the status of the main panel to a sub panel and you need 4 wire feed to subs. I may be totally wrong on this. My point is the main lug now becomes the first point of feed/service from the meter.

 

[dburoker]

So far the AHJ has said they will let me live with the existing 3 wire service. Without making too much of it I've been quite specific as to whether they'll allow the 3 wire service to stay.

At this point I'm going to get much more detailed with them when pulling the permit, so I'd like to be as informed as possible. Basically, I want to have reasonable answers to questions they may raise. Again, they've already said I could retain the 3 wire service.

I certainly don't want to look like I don't have a valid plan, giving them reason to reconsider the generous position on the existing house. My thinking is that by using a pass through panel, I'm essentially leaving the existing electrical paths unchanged.
The lugs on the load side of the meter and the MCB at the garage panel are "electrically the same point", to quote my old electronics instructor. I cant see how that changes if a pass through panel is inserted between them.

I could definitely see how they are no longer "electrically the same point" if a breaker were inserted between the meter and MCB at the garage panel, but that's not what I propose.

I know I'm trying to split hairs here, but they've said I can do it. I just need to have a reasonable position when I present plans for permitting.

Thanks again.

 

[pattenp]

I don't see any thing wrong with your plan if the AHJ will allow the 3 wire feed to come off the feed through from the main lug panel. The only reason I questioned it was because code can be interpreted in different ways by different AHJ's.

 

[dburoker]

Hi Pattenp,

Thanks for the quick reply. I wonder if others will feel the same as you and I. We'll wait a day or two to see the comments.

I wasn't going to push my luck too much with my AHJ... unless they offer that I can use 3 wire feed on the new wiring between the feedthrough MLO and the workshop, my assumption is that I will need to meet current code with my addition. No problem at all with that, though.

I'll go see my plans inspector late this week, after I've thought about this a bit more (or more honestly, after I see what kind of comments this post generates).

 

[pattenp]

After looking at 2011 NEC 230.82 you may need to add a disconnect between the meter and the MLO. That section says nothing but certain equipment can be mounted between the meter and the service disconnect. I don't see that the MLO is listed as allowed equipment. The only service disconnect I assume you have is in your current main panel.

 

[pattenp]

I'm sure you'll need to use 4 wire for the new feed to the shop.

I was thinking the AHJ allowed you to keep the 3 wire service because maybe they were thinking you were feeding the shop from the main panel and didn't know you were going to stick a new MLO in line.