It always makes my ebrow rise

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hardworkingstiff

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Wilmington, NC
I was at a marina today, and there was a 1200-amp panel there. (The panel is labeled 208Y/120-volt 3-phase 4-wire but is fed with 120/240 single-phase, they just didn't use C-phase).

The thing that really makes my ebrow rise is the panel was fed with 4 sets of 500 copper from an adjacent CT cabinet. The CT cabinet had one 3" conduit coming in from the transformer. I'd wager there is a (1) set of 350 aluminum in that 3" conduit.
 
Wow....I always like to "plan ahead" for the owner, and the POCO seems to dial all their sizing way down (they're so not sentimental about their gears' capacity), but that may be the biggest mismatch I've heard about yet.
 
dereckbc said:
NESC and NEC don't play by the same rules of the game.
Click to expand...

Yeah....I sometimes find meetings with POCO guys amusing as to how differently we do our demand factors.
 
My experience with marinas has the opposite type of mismatch for the panels. The boats that have the higher voltage equipment (usually A/C units or cooking equipment) call for 240 volts. So a 120/240 volt panel should be used. Instead the marina owners use 120/208 volt panels. So the A/C units overheat and the stoves take longer than they should to cook food.

Were the transformer and CT cabinet from the utility, or was the service point further upstream?

Also, were you asked to perform a service calculation, or do you at least know the number of slips and the types of receptacles at each slip? The fact that the 120/208V panel was rated at 1200 amps does not tell us whether a service (or feeder) of 350 AL is enough to handle the calculated load. As an example, if there were 24 slips and they only had one 125 volt, 30 amp receptacle at each slip, then the ampacity of a 350 AL service conductor is just 2 amps short of being enough to handle the load.
 
charlie b said:
Were the transformer and CT cabinet from the utility, or was the service point further upstream?

Also, were you asked to perform a service calculation, or do you at least know the number of slips and the types of receptacles at each slip? The fact that the 120/208V panel was rated at 1200 amps does not tell us whether a service (or feeder) of 350 AL is enough to handle the calculated load. As an example, if there were 24 slips and they only had one 125 volt, 30 amp receptacle at each slip, then the ampacity of a 350 AL service conductor is just 2 amps short of being enough to handle the load.
Click to expand...

Transformer and CT cabinet are from the PoCo. The engineer we hired was doing the load calculations. I'd bet there are more than 30 slips (I didn't cout) with 30-amp receptacles and a floating dockhouse. I'm pretty sure the 1200-amps is more than adequate, but I firmly believe the 350 AL (especially w/voltage drop) is tight.
 
I perform quite a few load surveys, monitoring for specified periods of time, it has been my experience (in my local area) that the services sized per the NEC have quite a margin of error, residential and commercial. There is a good reason for this, expansion and safety.

The utility, I believe; sizes their equipment to operate at close to full rating, based upon their specifications, not the NEC. They achieve a better efficiency and only once in 36 years have I seen a problem related to this sizing. The utility is out to save money, protect their investment and also have a concern for public safety; they have experience in this and for the most part seem to do an adequate job.

Recently we did emergency repairs in a building that had 2-4000 amp busways; we had to feed the whole building off one busway (the other busway blew up, catastrophic failure). Everyone was concerned about the full building load on the one busway. We brought the building online and the combined load on the one busway was 1650 amps, give or take an amp.

In the Washington DC metro area this is fairly typical in commercial office buildings, data centers well that something else.
 
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