Marinas

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Re: Marinas

Wayne I also wanted to apply 210.23 to to the pin and sleeve thread that I mentioned but a receptacle is not a load.

I know the load could be the rating of the receptacle but we can not apply the code to what may happen.

I look at it like saying a 200 amp disconnect with 125 amp fuses must be wired with 200 amp conductors as someone may change the fuses.

I still think it is usually a poor design to under feed a receptacle.
 
Re: Marinas

charlie when i take .3 times 2400 I get 720 not 740 but the service is the same anyway. did one of thes just recently for a yard with 72 outlets used for dry land storage of boats. worked great but all we had was single phase. AQnyway as a caveat to the receptacle question the reason people use 30 amp receptacles on the 15 and 20 amp breakers is because all marinco shore power cords for most boats from 24 to 40 ft use a 30 amp plug. Only the larger yachts 40+ ft use 50 amp. So the only reason is for convenience of plugging in. Nearly all marinas that have guest docks all have 30 amp outlets and I have seen many panels with 20 amp breakers serving the 30 amp receptacle. The load on boats is not really very large. In my case I have a 32 bayliner and with the small water heater ,lites, a heater and battery charger I will rarely if ever trip a 20 amp shore power breaker. I have looked at the loads with an amprobe on many boats in guest slips and have never found any drawing much more than 16 to 18 amp tops with most at 8 to 9. Nevertheless as my local inspector pointed out, the code does not allow 30 amp receptacles on 20 amp breakers per 551.19(A)(3). (Even tho its a common practice )
 
Re: Marinas

mike When you do the load calcs for each panel you will also be surprized how litle you can get on a 200 amp panel,. The panel laods are also calculated by the number of the receptacles x 120x30/(208xsqrt 3). for instance with 28 rfeceptacles the factor is .7 and you come up with 196 amps so the max on a 208 volt 3 phase 200 aMP panel would therfore be only 28 receptacles.
 
Re: Marinas

I think you ment 555.19 A (3) not 551.19 A (3) but in any event when #3 states voltage class and rating corresponding to the rating of the receptacle. Does it mean voltage class (208 or 240) and voltage rating (120 or 240) or voltage class and current rating. Your inspector must feel its the latter, but it could be interpretated either way couldn't it? And if it were voltage / voltage the 30A rec would be for convience or application only as stated above. You just can't put a 120V device on a 240V circuit. Just a different way of looking at it, but the AHJ has the last say when something is subject to interpretation!
 
Re: Marinas

Originally posted by stew: Charlie when I take .3 times 2400 I get 720 not 740 but the service is the same anyway.
Click to expand...
It was a typo, and it has been fixed. Thanks.
 
Re: Marinas

please take this as being taught to do it this way from some people that make up the masters test here. but somewhere in the calculation do you devide by the number of phases and use that number to size your service?
 
Re: Marinas

You do not divide by the number of phases.
</font>
  • <font size="2" face="Verdana, Helvetica, sans-serif">For a single phase, divide VA by the voltage, and you get amps.</font>
<font size="2" face="Verdana, Helvetica, sans-serif"></font>
  • <font size="2" face="Verdana, Helvetica, sans-serif">For a three phase, divide VA by the voltage, then divide the result by the square root of three, and you get amps.</font>
<font size="2" face="Verdana, Helvetica, sans-serif">You size your service on the basis of the amps, in either case. Perhaps the people you are talking with are not being clear in their explanations. Get them to show you the entire calculation, and have them point out where they are dividing by the number of phases.
 
Re: Marinas

I think the question of dividing by the number of phases may come from being taught th balance the load. If you look at Mike Holts electrical exam preparation book and his video tape series, he shows balancing the load across the phases and using the phase with the largest load (if I am not mistaken I haven't watched the tape for sometime now)this could be where the dividing by the number of phases comes from. Or at least the thought of dividing by 3!
 
Re: Marinas

if you look at mike holt's nec book he showws to balance the load but only uses 1 phase for the sizing of the service
 
Re: Marinas

from mike holt's book understanding the nec 2002 volume 2, pg.96
"what size 120/240v' single phase service is required for a marina that has twenty 20a, 120v receptacles and twenty 30a, 240v receptacles?

from the figure on the right
" 555.12 demand load based on number of receptacles, balance receptacles to determine maximum on any line.
line 1 line 2
20- 30a 240v receptacles 20 x 30a 20 x 30a
20- 20a 120v receptacles 10 X 20a 20 x 20a
total 30- 800a 30- 800-

t555.12 demand load for 30 receptacles is 70%-
800 x 70%= 560a demand load
the service is based on this 560a
the answer to his question is 600a"
 
Re: Marinas

I realize what mike holts book is showing. I was only trying to show that the way it was shown in the book for single phase could be looked at as dividing the load. If applied to three phase it could be taken as dividing by 3. No other point.
 
Re: Marinas

so then would the calculation from the question on page one of this post now be :

240 rec.'s / 3 = 80 rec.'s per phase
80 x 30a x 120v = 288000
288000 / (208 x 1.732) = 800a
t555.12- 30% 800a x 30% = 240a
next standard size breaker 250a
please tell if i'm wrong because the masters test here in maryland and most of the local jurisdictions are doing it this way

[ December 07, 2004, 05:04 PM: Message edited by: hcecabigdog ]
 
Re: Marinas

big dog . The way I would do the calculation you have shown is 20x20=400+20x30=600 for a total of 1000x120=120,000va. divide this by 240 and you get 500 amps. Multiply by the demand factor for 40 total receptacles which is .60 and your total service requirement is 300 amps. spliting the load equally would work well with 10 of the 20 amp and 10 of the 30 amp plugs each on their own 200 amp panel. this would result in a calculated load of 175 amps per panel.10x20=200+10x30=300 for a toatl of 500x120=60000divided by 240=250 x by demand factor for 20 receptacles of .7 for the total panel load of 175 amps. anyhow thats how I would figure it.. Joe

[ December 07, 2004, 10:23 PM: Message edited by: stew ]
 
Re: Marinas

I stil think my inspector was correct in his interpretation of the article 555.19(A)(3). Its says voltage class And rating. So then the correct voltage type must be used as well as the correct amperage rating and that is how I read the article as well.
 
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