Electrical question????

[relief]

what if his main is only 100 amp or 125?

90 percent of all US dwellings have 200 amp service, some have more some have less, so the assumption will most likely proove to be right. If the original poster could not grasp this simple concept, then by all means he should not be wiring a sub panel himself.

The service panel/meter box or both by NEC code must have a disconnect rated for the service of the dwelling (not rated lower either). 200 amp will have a 200 amp disconnect and so on, so he must disconnect the service power before installing the sub panel.... if he does not know the difference between a 200 amp, 100 amp service and so on then original poster does not have the grasp of the subject at hand to due the job himself.

Common sense tells someone take away 40 amps from what ever the service rating (x) gives you amps left over.

x - 40 = y

Besides, he's already pulling AT LEAST 30 amps with the 15 amp run and the extension cords. Im sure 40 amps will not effect his current amperage usage. Common sense.

 

[madpenguin]

240 volts x 40 amps = 9600 watts

You could run 9 1000 watt lights (8 would be safer) and use the existing 15 amp run for your fans and pumps.

Actually 7 is the max you can run. 9600 x 0.8 = 7680 (or more properly 32A)

That would leave you 680w for misc equipment assuming a 1000w ballast actually draws 1kw.

I'd also wager that more like 50% (or less) of US homes have a 200A service and probably 80% of all US Apartments have 60A service.... And probably 30% of all residences in the US utilize Knob & Tube wiring.

 

[relief]

Actually 7 is the max you can run. 9600 x 0.8 = 7680 (or more properly 32A)

He will be just fine with 8

9600 x .84 = 8064 and that is if each lights hits 1000 watts as you said.

That would leave you 680w for misc equipment assuming a 1000w ballast actually draws 1kw.

He's already running his misc equipment on an existing 110 ~ 120volt 15 amp run, therefore he can continue to use that existing run in his walls. No need to buy wire to run from the sub panel to the expensive junction boxes and/or plug outlets... not to mention a new breaker to put in the sub panel which would throw his 40 amp breaker at the service panel if he hit 8 ~ 10 amps assuming he takes either advice and is using 32 or 33.3 amps. Common sense should prevail. The advice I gave him will save him the most money and work.

I'd also wager that more like 50% (or less) of US homes have a 200A service and probably 80% of all US Apartments have 60A service.... And probably 30% of all residences in the US utilize Knob & Tube wiring.

A wager it is then, because there is no official source. You go by what you see in the field. I've been doing this for 34 years and I've worked in 42 of the US states and the VAST majority of residential service has been 200 amp service. Even you use "probably" when it comes to apartments and probably in continuance with your argument... which in itself isn't a very strong argument.

 

[madpenguin]

Not sure what your 0.84 is about but my point was continuous load, as I'm sure your aware. If your even 1 watt over a new circuit is called for. Just about everything in a grow room will be running for more than 3 hours at a time, so a #8AWG NM-B feeder should never see more than 32A, which would equate to 7680w @ 240v. Running 8kw as you suggest would be in direct violation of 210.19(A)(1), much less 9kw as you first stated.

 

[madpenguin]

The service panel/meter box or both by NEC code must have a disconnect rated for the service of the dwelling (not rated lower either).

Really not trying to be a dick but this is wrong too. I could feed a 125A MLO panelboard with 1/0 AL but yet use a 60A breaker for the disconnect. Panel, cable and breaker are all at different ratings there. Perfectly fine. You size everything according to the OCPD (breaker). You can also use #6 CU to feed that same 125A subpanel as long as the breaker is sized according to the wire.

So... A 200A service can have a 100A disco on the outside of the house. As long as the cable feeding the main panel is rated for atleast 100A...

Altho I think your statement is still correct after reading it more thoroughly... Sorry. Just clarifying then...

 

[groady-ho]

The formula is:
P = V * I

P is power in Watts
V is voltage in Volts
I is current in Amps

Watts = Volts times Amps

 

[madpenguin]

Ohms Law is good for resistive loads but when your dealing with inductive loads such as ballasts always look for the nameplate rating first. As Relief and I were saying, a 1000w lamp/ballast rarely draws 1000w. Use the nameplate specs. That's why they are there.

And just to clarify for others, all lighting is a continuous load. Air conditioners, Furnace's, water heaters, baseboard heaters... Anything that has the ability to run 3 hours or more you must derate to 80% of the conductor ampacity. That's where the 32A comes from. That doesn't mean you can use 33.3A or 32.5A or even 32.01A..... 32.00A max for a continuous load where #8AWG on a 40A breaker is involved.

You can also size the breaker/wire to 125% of the actual load. You'll get the same exact number if you did 80% of the conductor rating. 32A x 1.25 = 40A or 40A x 0.8 = 32A

If I had 4500w of baseboard heaters running at 240v that gives me 18.75A. I must use #10AWG cable to wire them, not #12... You also must use a 30A breaker to feed them. The conductors and breaker need to be derated. 80% of 20A is 16A so I'm over. 80% of 30A is 24A.

 

[madpenguin]

Dont run 3 on one run as there is start up surge that will most likely throw your breaker.

I really hate to keep picking on you, it's nothing personal. Seriously, I mean it. That's general misinformation tho. A 15A breaker can handle way more than 15A for a limited time. They are designed that way. If you draw more than 15A for more than a couple seconds, then it will kick.

In your example, you wouldn't want to run 3 600w's @ 120v because it puts you over the 12A limit for a continuous load on a 15A circuit, not because of inrush current (LRA). Your statement implies that one could use time relays so all 3 ballasts start a couple seconds apart, thus making everything O.K.... Not so.

 

[Blunt_69]

3 600 watt lights is not enough comfort zone on a single 15 amp breaker.

People should just run 240 volt service via subpanel when going over 2 lights in any situation.It's safer and resistive cord runs(ie extension cords) are kept at minimal lengths because sockets are near by.

 

[Brazilianfire]

Thank you RELIEF for all your professional input! I do grasp the sub panel concept, a buddy of mine made one and so far smooth sailing. So it is the best way it seems. I have seen fires from stepping up amperage on breakers and will never do that.. Relief, I posted a question about a wire schematic on here, if possible please let me know if you can assist. Thank you.

 

[Wait...What?]

90 percent of all US dwellings have 200 amp service, some have more some have less, so the assumption will most likely proove to be right. If the original poster could not grasp this simple concept, then by all means he should not be wiring a sub panel himself.

The service panel/meter box or both by NEC code must have a disconnect rated for the service of the dwelling (not rated lower either). 200 amp will have a 200 amp disconnect and so on, so he must disconnect the service power before installing the sub panel.... if he does not know the difference between a 200 amp, 100 amp service and so on then original poster does not have the grasp of the subject at hand to due the job himself.

Common sense tells someone take away 40 amps from what ever the service rating (x) gives you amps left over.

x - 40 = y

Besides, he's already pulling AT LEAST 30 amps with the 15 amp run and the extension cords. Im sure 40 amps will not effect his current amperage usage. Common sense.

You're insane if you think 90% of the homes in USA have 200 amp service. 90% of the homes built in the last 10 years maybe

but there's still plenty of homes, including mine, that are still 60amp. 100amp is required if you want to sell otherwise the buyer cant get insurance. But 200amp? Only a modern McMansion comes with that kind of meter.

I suck a 1kw, two 600, and a 400 through plug fuses And my home is in a metropolitan area with over 6 million people so its not like im out in the sticks. Just plain old suburbia.

 

[Brazilianfire]

he did say some will have more and less.. just a thought.

 

[Wait...What?]

Oh i know, I'm just sayin his premise might be skewed a bit, thats all. nothing personal, and its only an opinion. If you dont like it, discard it.

smilies because inflection doesn't come through well in a textual medium.

 

[Brazilianfire]

I value ALL opinion , thank you

 

[Wait...What?]

He's dead on, on the rest of it though. So count my post as nonsense, i guess...