Is it 800A service or 350A service?
- Thread starter maint314
- Start date
- Status
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
My guess is it is 800 amps and only 350 amps is being used from the mdp.
- Location
- Massachusetts
First off it is not a service it is a feeder. 
To me it looks like there is an existing 800 amp panel owned by the landlord.
The new work requires a 350 amp breaker be installed in the landlords panel, a set of 500s run to the new MDP that contains a 350 amp main cb.
I would call this a 350 amp feeder.
To me it looks like there is an existing 800 amp panel owned by the landlord.
The new work requires a 350 amp breaker be installed in the landlords panel, a set of 500s run to the new MDP that contains a 350 amp main cb.
I would call this a 350 amp feeder.
- Location
- New Jersey
- Occupation
- Journeyman Electrician
First off it is not a service it is a feeder.
To me it looks like there is an existing 800 amp panel owned by the landlord.
The new work requires a 350 amp breaker be installed in the landlords panel, a set of 500s run to the new MDP that contains a 350 amp main cb.
I would call this a 350 amp feeder.
I agree, the stuff on the roof is depicted with dashed lines typically indicating an existing piece of equipment.
The equipment on the roof is a transformer with a panelboard mounted to it. The panel board has 5 different breakers on it. The one leading to this suite has 800 printed on the handle. Thats why I thought it was an 800A feed(service) to this suite. I thought the MDP panel was only rated to the load the suite would be using which is 350A, even though they have made 800A available.
- Location
- Massachusetts
Well you did not tell us that.
That seems like an issue unless it is an 800 amp frame size with a 350 amp trip unit.
Or unless the 800 is the roof panels main breaker which seems much more likely.
As far as service vs feeder it makes a big difference in the rules. The thing to remember is a service only comes from a utility it never can come from a customers panel.
I apologize for not giving you enough info. Im learning here. Still pretty new to maintenance. The panelboard is rated to 1600A. The 800A breaker is just for this suite. Thats why I think it's 800A feed. I just didnt get why the panel in the suite "MDP" is only 350A. Shouldnt it be 800A panel since it's an 800A feed to the suite? Or is the panel only rated for the max load the suite is putting on the circuit. So if that only 350A panel, does that mean there is still 450A available for use on that circuit?
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
If the overcurrent protective device and the wire is arted 800 amps that feeds the panel then the panel should be rated 800 amps also.
- Location
- Massachusetts
No problem at all.
As we all are here.
The roof panel bus bars may well be rated 1,600 amps but the print you posted shows that the roof panel is 800 amps. Likely that means it has an 800 amp overcurrent device ahead of it. The main might be a backfed breaker.
How do you know that? It is not what the prints indicate.
The print shows a feeder from the roof panel to the MDP that is rated 380 amps not 800.
The feeder has just four - 500 kcmil (I will assume copper) and they are rated 380 amps. The largest breaker allowed would be a 400, not even close to 800.
Could be an 800A breaker in roof panel. Drop to the suite MDP would be a feeder tap. But the #3 EGC is an indication it is not.
- Location
- Massachusetts
Yes, it could be a lot of things,
maybe the conductors are super conductors. Or maybe they are encased in concrete from the roof to the panel and the #3 is unused. But I am just a KISS kind of guy and go with the most likely based on my personal experiences.
Others experiences are likely to vary.
.
Here is the panel mounted on the roof. The 3rd one down is it. When I throw it it shuts down "MDP,A, and RTU 2" located in the suite. The breaker has 800A labeled on it. MDP is labeled and show on the print 350A. Why is there a 350A panel feed from a 800A. If this 800A breaker on the roof feeds 2 suits then would only 400A be available to each suite? That would explain the 350A "MDP" panel. This is a great discussion. Thank you.
none of the above
Electric-Light
Senior Member
That's not how it works. There are formulas and tables EEs use to determine how it is sized. Look at the breakers in your house. Yes, they add up to higher value than the service.
Go up another rung in the ladder.
Say each house is 200A and there are 10 houses to the transformer. If you just add things up, the transformer would have to be 480kVA, but there is no way you'll see a 500kVA transformer for a block with 10 house.
Yes, a coordinated block wide effort at the block level to get each house to turn on 40kW of all once will trip something or damage PoCo equipment.
There are formulas that address things at the individual building, block, subdivision level and in larger level. The formulas don't stay good forever, because of cultural change.
When the existing power system was designed, the coincidence factor did not consider modern, high demand customer loads such as electric car charging, tankless electric water heaters or practically every house having an A/C.
- Location
- Massachusetts
OK, but did you see if it also shut down anything else?
There should not be a 350 amp panel and feeder protected only by an 800 amp breaker.
That is what leads me to believe you are mistaken ... OR it has been wired wrong but with real prints that seems unlikely.
Forget about 'whats left' there is no way to tell from the info you have shown us to figure out what capacity has been used or is left.
The breaker handles are meaningless to figure out the capacity of the panel. You would need to know the calculated loads.
Can't read it in picture. It's the number in the little 'window' off to side of handle.
If it has 800 in it, you need to RFI the Engineer of Record (or indirectly through GC if subbing).
Electric-Light
Senior Member
iwire,
can I get the user title "Light Emitting Decoration" ?
can I get the user title "Light Emitting Decoration" ?
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