Can someone help me grab the concept of this 320 amp service debacle. From what I understand a 400 amp meter socket is actually a 320amp meter socket because of the 80% rating. So is a 400 amp load enter only rated for 320 amps? On our parts we need to ct meter a 400 amp service. But we can use a 320amp meter sockets for other installations. :? Is it only a true 400 amp service if it's ct metered
320amp vs 400amp
- Thread starter fireryan
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jumper
Senior Member
- Location
- 3 Hr 2 Min from Winged Horses
The rating is 320 continuous or 400 non conti uous or a combination of both with continuous x 1.25 + non continuous for 400.
So yes a 320 meter is for a 400A service which is usually a combo load.
kwired
Electron manager
- Location
- NE Nebraska
If the meter is a plug in meter it is 320 amp.
If it bolts in (those seem to be pretty rare but are some out there) it is 400 amp or even higher. Most POCO choose to use CT metering though for anything over 320.
jumper
Senior Member
- Location
- 3 Hr 2 Min from Winged Horses
Are you saying I cannot use a 320A plug in meter for a 400A service. I am pretty sure the meters are rated for continuous duty.
mwm1752
Senior Member
- Location
- Aspen, Colo
service calulations are at 100% with continuous & non continuous loads included -- the 320 meter is good for a 320 amp service load & yes I believe they are the largest line type plug in without going to a CT monoriting system.
kwired
Electron manager
- Location
- NE Nebraska
My opinion - it is up to the POCO what you will use in most instances.
Once had one that wanted me to install a bolt on type meter can for a 480/277 400 amp service. They later decided to take the guts out of it and install CT's and cap the hole where the meter goes.:roll:
Carultch
Senior Member
- Location
- Massachusetts
How does this work if your load is dominated by non-continuous loads?
Are you limited to a total of 320A = 100% non-continuous + 100% continuous for a continuous duty rated meter (and other similarly rated products)?
Or are all continuous duty rated products meant to be sized by 80% of (100% non-continuous + 125% continuous)?
- Location
- Massachusetts
Yes, all the time.
Frank DuVal
Senior Member
- Occupation
- Electrical Contractor, Electrical Engineer
Around these parts, it is a 320 meter socket (called 400 amp by power company) feeding two 200 amp panels in residential service. Typical Mcmansion, two to three HVAC heat pumps. We are a moderate climate, so heat pumps outnumber gas/oil fired heat.
see this is where this gets me. With our power company a 400amp service must be ct metered in a termination cabinet. But according to there specs I can use a 320amp meter socket for a service. If I can put a 400amp panel off of a 320amp meter socket why would I ever want to install a ct cabinet? Ask I missing something here? Because with a CT cabinet I'm still not getting a full 400amp service because the main breaker is only rated at 80% correct?
jumper
Senior Member
- Location
- 3 Hr 2 Min from Winged Horses
There is no 80% rule per se.
.8 is the inverse of 1.25, continuous loads are multiplied by 1.25 or if you wish, breakers are loaded 80% of a continuous load.
The breaker is rated the same by the same rules as noted earlier for the meter socket.
100% of non continuous load
80% of continuous load.
or a combination of both, 400A in your case.
Carultch
Senior Member
- Location
- Massachusetts
The question I'm asking is on a similar note.
With 320A for an entirely continuous load of 320A, the service would be 400A with a 400A main breaker, and we know a 320A meter base is all that you'd need.
However, given 400A of entirely non-continuous load for a 400A service and 400A main breaker, is a 320A meter socket still sufficient?
jumper
Senior Member
- Location
- 3 Hr 2 Min from Winged Horses
If your load was continuous you could only load the breaker 80%, because you would have to multiply the load by 1.25.
Carultch
Senior Member
- Location
- Massachusetts
jumper
Senior Member
- Location
- 3 Hr 2 Min from Winged Horses
MrNiceberg
Member
- Location
- Minnesota
From what I've been told. It is technically a 320A meter socket, but people install 2 - 200A panels off of it all the time...resulting in the "400A" name. Not saying that is correct, just passing along the information. Also...I am still an apprentice...so there's that... :blink:
- Location
- Massachusetts
I have read your question and I don't know what you are asking.
jumper
Senior Member
- Location
- 3 Hr 2 Min from Winged Horses
See if the helps for determining the load:
230.42 Minimum Size and Rating.
(A) General. The ampacity of service-entrance conductors
shall not be less than either 230.42(A)(1), (A)(2), or (A)(3).
Loads shall be determined in accordance with Part III, IV,
or V of Article 220, as applicable. Ampacity shall be determined
from 310.15. The maximum allowable current of
busways shall be that value for which the busway has been
listed or labeled.
(1) The sum of the noncontinuous loads plus 125 percent
of continuous loads
(2) The sum of the noncontinuous load plus the continuous
load after the application of any adjustment or correction
factors.
(3) The sum of the noncontinuous load plus the continuous
load if the service-entrance conductors terminate in an
overcurrent device where both the overcurrent device
and its assembly are listed for operation at 100 percent
of their rating
230.42 Minimum Size and Rating.
(A) General. The ampacity of service-entrance conductors
shall not be less than either 230.42(A)(1), (A)(2), or (A)(3).
Loads shall be determined in accordance with Part III, IV,
or V of Article 220, as applicable. Ampacity shall be determined
from 310.15. The maximum allowable current of
busways shall be that value for which the busway has been
listed or labeled.
(1) The sum of the noncontinuous loads plus 125 percent
of continuous loads
(2) The sum of the noncontinuous load plus the continuous
load after the application of any adjustment or correction
factors.
(3) The sum of the noncontinuous load plus the continuous
load if the service-entrance conductors terminate in an
overcurrent device where both the overcurrent device
and its assembly are listed for operation at 100 percent
of their rating
- Location
- Massachusetts
If you buy a standard 400 amp panel it is also rated 320 amp continuos and 400 amps non-continuos.
If you buy a 200 amp panel it is rated 160 amps continuos and 200 amps non-continiuos.
Use two 200 amp panels and you get 160+160 continuos and 200+200 non-continuos
All three of my examples are rated the same as a 320 class meter.
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