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Old 06-02-2008, 01:36 PM   #1
Des
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Max amps allowed - electrician advice needed


Hi all.

I have what I think is a basic question and I just need a little expert input which would be greatly appreciated.

I have a dedicated 20 amp circuit for an aquarium.
12/2 wire, 20 amp breaker and 20 amp GFCI outlet.
The total run is about 50 feet.

The aquarium has about 3.5 amps worth of equipment that is always running. Pumps and such that are on a shared circuit.

The 20 amp dedicated circuit is for lighting and a chiller and some fans.
The Lighting consists of 500 rated watts of metal halide on a magnetic hqi ballast. Also about 160 watts for T5 flourescent. 3 fans switch on with the lighting, one is on a temp controller and is actually the only device on this circuit that runs all day, on and off, along with the chiller, which is also on a thermostat/controller and cycles on an off all day.

The flourescent lighting is on from 12 noon to 11pm.
The halides run from 3 pm to 10 pm.

When all the lighting is running along with all the fans the total amperage draw is right around 9 amps continuous. The flourescents pull a hair over 2 amps, the halides about 6 amps (actually draw close t0 640 watts) and the fans another amp. A Kill-a-watt meter measures the total at 9.1 amps.

When the Chiller kicks on and settles in after 30 seconds to a minute or so (1/3 hp chiller) the total amp draw is just under 16 amps. The Kill-a-watt measures it at 15.7 amps. This is with EVERYTHING running on the circuit.

The Chiller runs for about 45 minutes per cycle and cycles on and off maybe 3 or 4 times while all the lighting is also on. So that 15.7 amp total would only occur 4 times a day at the most and for 45 minutes each of those 4 times. Of course it will cylce on and off a few more times each day and night but the halides would not be on at the same time so the draw would be atleast 6 amps less at all other times when the halides are off.

Im sorry about the long explanation but I want to make sure my whole situation is covered and explained as well as I could.

I know that 16 amps would be 80% of the 20 amps and it is my understanding that a circuit should not be loaded beyond 80%. So I am close but if the meter is close to accurate I should be just below the 80%
But I have also read that the circuit can be 100% loaded as long as nothing runs it to fill 100% for more than 3 hours continuous.

So my question is ... first, which is correct, the 80% or the 100% (if under 3 hours continuous)?

Either way, am I ok being just barely below the 16 amps on the dedicated 20 amp circuit, especially seeing that it only runs near the 16 amps for 45 minutes or so, four times per day?

Or do I need to remove a couple of amps ? I can pull the flourescents off the 20 amp circuit and place them on the shared 15 amp circuit which would bring that up to 5.5 amps when the flourescents are on and drop the dedicated circuit to a maximum of just below 14 amps. The shared circuit is shared with the living room and I think I am well within the limits of this 15 amp circuit now. I doubt that the 2 amps additional would matter. But i would rather keep the flourescents on the 20 amp dedicated of you professional electricians feel it is ok.

Once again, I appreciate any advice. Thanks in advance.

Des

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Old 06-02-2008, 01:52 PM   #2
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Max amps allowed - electrician advice needed


Not an electrician but I do have a reef. You should consider having more than 1 circuit for the tank. Put your main pump on one circuit and a few powerheads on the other. If you're ever not home and the circuit trips, your tank won't spiral out of control from lack of O2.

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Old 06-02-2008, 02:04 PM   #3
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Max amps allowed - electrician advice needed


Ditto that. I'd definitely put circulation pumps on two separate circuits in case one trips. You're running the entire tank on a single circuit through single GFI, as far as I can tell, and if either of those tripped, you'd probably have coral or fish deaths in a couple hours on a warm day.

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Old 06-02-2008, 02:05 PM   #4
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Originally Posted by Clutchcargo View Post
Not an electrician but I do have a reef. You should consider having more than 1 circuit for the tank. Put your main pump on one circuit and a few powerheads on the other. If you're ever not home and the circuit trips, your tank won't spiral out of control from lack of O2.

Thanks, but I do have two circuits as I layed out in my message. Also battery backup on my circulation so I am ok.
I appreciate it.

Just need the dedicated circuit load advice for now.

Thanks
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Old 06-02-2008, 02:14 PM   #5
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Max amps allowed - electrician advice needed


You should be fine but as clutch said, if you can split some things up you'd be better off. And yes "continuous" is 3 or more hours. Also, is your receptacle a 20 amp receptacle? Nevermind, I see now you said a 20 amp gfci

Last edited by wirenut1110; 06-02-2008 at 02:33 PM.
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Old 06-02-2008, 02:42 PM   #6
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Max amps allowed - electrician advice needed


I have nothing to add but, I just wired a BIG aquarium

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Old 06-02-2008, 04:15 PM   #7
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Originally Posted by wirenut1110 View Post
You should be fine but as clutch said, if you can split some things up you'd be better off. And yes "continuous" is 3 or more hours. Also, is your receptacle a 20 amp receptacle? Nevermind, I see now you said a 20 amp gfci

Thank you wirenut. Thats what I needed to know.


I cannot run another dedicated circuit without having a new main breaker box installed which isnt an option.
I do have 2 outlets as I have mentioned. The second outlet is 15 amp and shared with the living room and I cant really load it any further than a couple more amps. I am not worried about power outage or tripped breaker as again, my in tank circulation has batter backup. Im good guys.

I may move the return pump to the 20 amp though as it also feeds the chiller and if I lose power on the pump the chiller will short cycle. Which means I will need to move the flourescents to the shared cycle to prevent overloading the dedicated.

Thanks again for the input.
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Old 06-02-2008, 04:19 PM   #8
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Max amps allowed - electrician advice needed


You could always add tandem breakers if your panel allows it and doesn't have the max number of circuits in it already.
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Old 06-02-2008, 04:46 PM   #9
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Originally Posted by 220/221 View Post
I have nothing to add but, I just wired a BIG aquarium

OMG...what a lousy job!...can't you see the lamp that's not level?


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Old 06-03-2008, 09:22 AM   #10
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You could always add tandem breakers if your panel allows it and doesn't have the max number of circuits in it already.
I havent seen tandem breakers for the box we have, it's a Cutler Hammer.
There are a few breakers spaces available. The Problem is that the neutral/ground bar in the box is full. Actually, the way they attached the main ground lug and a couple other things, they are actually blocking a few of the set screws. So anyway, the only way to add another circuit would be to share a space on the ground bar for the neutral and ground wires with another circuits ground and neutral. In other words, I'd have to share a space for the neutral with an already existing neutral from another circuit and same for the ground with an existing ground from another circuit.

They are obviously all on the same bar together in the box anyway so I dont see how it would matter but I assume there is some code or some other reason why you cant do that.
If Im wrong, an it is fine to put two different neutrals and grounds under the same set screw on the neutral/ground bar then I can add another dedicated circuit. As I said, there are several breaker spaces available still.

So, whats the rule on this?

Thanks

Last edited by Des; 06-03-2008 at 09:24 AM.
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Old 06-03-2008, 11:10 AM   #11
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Max amps allowed - electrician advice needed


Quote:
Originally Posted by Des View Post
I havent seen tandem breakers for the box we have, it's a Cutler Hammer.
There are a few breakers spaces available. The Problem is that the neutral/ground bar in the box is full. Actually, the way they attached the main ground lug and a couple other things, they are actually blocking a few of the set screws. So anyway, the only way to add another circuit would be to share a space on the ground bar for the neutral and ground wires with another circuits ground and neutral. In other words, I'd have to share a space for the neutral with an already existing neutral from another circuit and same for the ground with an existing ground from another circuit.

They are obviously all on the same bar together in the box anyway so I dont see how it would matter but I assume there is some code or some other reason why you cant do that.
If Im wrong, an it is fine to put two different neutrals and grounds under the same set screw on the neutral/ground bar then I can add another dedicated circuit. As I said, there are several breaker spaces available still.

So, whats the rule on this?

Thanks
You CANNOT put 2 neutrals under the same screw. You CAN put grounds together, so long as the panel's bar is rated for it.
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Old 06-03-2008, 03:29 PM   #12
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You CANNOT put 2 neutrals under the same screw. You CAN put grounds together, so long as the panel's bar is rated for it.

Ok, so that means that all I would have to do is combine a couple of grounds which would free up a position for a neutral, right?
Or am I missing something?

Also, if you dont mind, can you explain why it matters if a couple of neutrals are combined together under the same screw when both neutrals and grounds are all connected on the same ground bar anyway?
Im not doubting you at all, I just am missing what difference it makes.

Thanks
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Old 06-03-2008, 05:48 PM   #13
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Max amps allowed - electrician advice needed


Dude,

The neutral is a current carrying conductor and will heat-up when there's current flow so the conductor needs to be connected all by itself to the bar. Imagine the tiny point of contact between the wire and bar, when you have two wires the amount of heat is doubled and is not allowed. On the other hand, the ground wire doesn't have current flowing through it. The ground wire is a return path only when there's a fault to ground, so when that happens the breaker will trip really fast and no heat will accumulate due to current flow.

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I'm kinda dumbfounded, There's not two separate bars in the panel? I've never seen neutral sand grounds all tied to the same bus. hmmm?
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Old 06-03-2008, 05:52 PM   #14
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Max amps allowed - electrician advice needed


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I'm kinda dumbfounded, There's not two separate bars in the panel? I've never seen neutral sand grounds all tied to the same bus. hmmm?
Seriously? This is absolutely typical in the US. Many older main panels had only one bar.
Newer stuff has two bars that are bonded.
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Old 06-03-2008, 06:24 PM   #15
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Max amps allowed - electrician advice needed


I just wanted to throw my 2cents into this, first off, dont even worry about the 3 hour continuous duty since it does not apply to your situation, also, IMO, a 20 amp circuit is more than adequate for the setup you described.

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