number of lights on a circuit

how many 400 W lights can I run on one circuit?
I read before that 400W hps lights use about 4 amps, on the ballast it seems to say that it only uses 1.8 or somthing, but almost for on a short circuit, I dont know what that really means... I think it means I can run more than 4 lights if I start them 2 at a time?
help me, I'm a high lost sole.

you should be fine as long as your growroom is the only thing on that circuit...

Most circuits are 15 amps, check your breakers because some of the newer houses may be 20, the standard is 15.

Take you 1.8 amps and divide it by 15 amps and you get 8.33333 lamps on one circuit.

If you want to learn some about electricity, go and look up OHM's LAW. IT will help you alot.

tckfui said:

how many 400 W lights can I run on one circuit?
I read before that 400W hps lights use about 4 amps, on the ballast it seems to say that it only uses 1.8 or somthing, but almost for on a short circuit, I dont know what that really means... I think it means I can run more than 4 lights if I start them 2 at a time?
help me, I'm a high lost sole.

Click to expand...

first piece of advice - only listen to an electrician for electrical questions
second piece of advice - i am not an electrician
third piece of advice - a 400 watt light uses slightly more than 400 watts, at 110 volts equals about 4 amps. the 1.8 you can ignore.

if you were asking how many bulbs can you use with one ballast, the answer is one.

if you were asking how many 400 watt systems can you run on one standard house circuit, the answer would be 3:

440 watts/110 volts = 4 amps.
house circuit = .8 x 15 amps = 12 amps (80% safety factor in circuit breakers)

number of lights = 12/4 =3 if you don;t have anything else on the circuit

if you need more lights go 240. you can get about 10 400w on a 30 amp. dryer breaker

I think I may have a dryer breaker... how do I know? its on the same circuit as my washer, and dryer, I only use one light or none when doing laundry, when I use two I blow a fuse... so stoped doing that after the first time
I only want to use 3 for now, but possibly 4 in the near future.
the plug in the wall is a three prong plug but with like a sidways T for the right prong... does that help

A house in the US that has new electrical (not antiquated or old) can run up to approx 10000 watts.After that you need to have the electric company come and do an upgrade and put another box in. There are plenty of people that run 18 600 watt lights and run all the other appliances at the same time.hope this helps

peace

but that's on several circuits, I want to know how many I can put on one single circuit.
and my house is pretty old, at least 80 years old, but this part of the house is only 25 or so.

This I can tell you, having built the upstairs of my old house in Memphis and wiring everything exactly to code - just had the electrician come in and certify everything.

Best way to check is to get a regular lamp, plug it in the room you're going to use/tap power from. Turn it on, flip breakers until that light turns off. Look at that breaker switch that turned off the light, you should see either 10, 15, or 20. Take whatever number you find, multiply by 110. That'll tell you how many watts that circuit can hold before tripping. if you're running a 400w bulb, allocate 500w, so divide the big number you got by multiplying the breaker number by 110, and divide by 500. That'll give you the maximum you want to put on that circuit.

Also, the type of ballast will matter greatly - magnetic ballasts are a hellacious inductive load, whereas digital ballasts are not so power-hungry. If you've got magnetic ballasts, I'd suggest a staggered-start on the timers, because all of those lights coming on at the same time would likely trip the breaker safety. Set them to come on two minutes apart if you're using magnetic ballasts.

watts / volts + amps
volts * amps = watts
just 2 of the rules in PIER chart / ohms law.
national electrical code allows for loading lighting circuits to 85%
and you need actual voltage not just 110 or 120 if you are on a long run far from the transformer you may only have 105 volts. but for now we will assume you have 118 volts. which is pretty common.
and ill show you a 20 amp and a 15 amp circuit.
a 15 amp circuit loaded to 80% is 15 amps * 118 volts * 80% = 1416 watts at 80%
and 20 amps * 118 volts * 80% = 1888 watts

a 15 amp circuit has 1416 watts available at 80% so 1416 / 400 = 3.54 so on that 15 amp circuit you can run 3
on a 20 you have 1888 watts available at 80% so 1888 / 400 = 4.72 so that 20 amp will allow 4
and these numbers are only for dedicated lines. if you have other lights or outlets on the circuit it could drastically reduce the number of 400 watt lights you could run on it
woops forgot continuous load is 80% redid the math sorry
Continuous Load. "A load where the maximum current is expected to continue for 3 hours or more." (That is the maximum running current, exclusive of starting current.)

desertrat said:

first piece of advice - only listen to an electrician for electrical questions
second piece of advice - i am not an electrician
third piece of advice - a 400 watt light uses slightly more than 400 watts, at 110 volts equals about 4 amps. the 1.8 you can ignore.

if you were asking how many bulbs can you use with one ballast, the answer is one.

if you were asking how many 400 watt systems can you run on one standard house circuit, the answer would be 3:

440 watts/110 volts = 4 amps.
house circuit = .8 x 15 amps = 12 amps (80% safety factor in circuit breakers)

number of lights = 12/4 =3 if you don;t have anything else on the circuit

Click to expand...

like desert rat i am not an electrician either...but his info is solid...his example of dividing watts by volts to get amps and multiply amps by .80 is the correct formula...i have been in remodeling part time all my life and that is one of the most helpful and overlooked formulas needed...also if you run your own complete circut make sure to use the correct wire size...14 guage is good for 15 amps...12 guage is good for 20 amps...this is for 110-120 volt circut...good luck

okay, so alittle confused now.
I found out that there are aparently 2 circuits? maybe one fancy one, I dont know. I may post some pics if I cant describe it.
so on my circuit breaker, there are a bunch of switches, mostly saying 15 amps, one says 30, and 2 say 20, I never saw a 30 amp one but I guess I have one somewear in here? but anyway... I have 4 circuit breaker boxes, as I live in a 3 family house and I have everyone meters and circuits in my house, so on one of the two that are mine, there are 8 slots for a cuircut, but only 7 are full, one empty, but two slots have like a double switch... does this mean that there are two circuits on the one? or what? the right of the two switch cuircut shuts off the ceiling light, and that apears to be it, the left one shuts off the outlets, pics comming soon.
does this mean I have 20 amps at my disposal? or are the 2 switches combined 20 or what?

The 30 amp very likely runs your washer and dryer, and maybe your water heater as well.

The double-sized breakers are just double-sized breakers - whatever number is on them that's what they're rated for.

Re-read my first post here in this thread, and you should be set to go.

well I turned my dryer on and fliched all the switches to find which cuircut the lights are on, as they are in the same outlet. so I can run 4 lights? party time?
no pics needed?
thanks man

just remember to add 25% to your ballast wattage (if it's 400w assume 500+ load on startup) so you don't overload your circuit with many ballasts starting up at once

I'm thinking I'm just going to use 3,
according to "Newschool Indoor Growing" a 400 W HPS can efficiently cover a 16 square foot area, this area is just about 32, feet, so 3 should be more than enough.
but I've read various numbers on how many square feet a 400 watter can cover. but I figure 3 should be plenty, and if not, theres always next crop
thanks guys! I think I'm set... now if people would just help me in my nute thread!