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Old 24-08-2014, 05:50   #16
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Re: Adding a 2nd AC input

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Originally Posted by Toubab View Post



I understand this, but am I supposed to cut open my shore power cable? Or the cable coming out of the plug on the inside of the boat? Neither of those things seem like a great idea... it just seems like an invitation for water and corrosion in my electrical system. Am I missing something?

Thanks so much for your help! I'm sorry if I'm asking really dumb questions but I'm trying to learn as much as I can.
Since you ask this question I will assume you have triplex wire throughout the boat. You should be able to clamp onto the wires at the main breaker and the breaker for each circuit. They should be separated down to one wire at these locations. You can clamp on anywhere the outer covering has been removed exposing the white, black and green wire where you can get the clamp around the hot wire.

With all your stuff on and running, carefully clamp onto the wire at each breaker and see what amps are going through each circuit. Report your findings here.

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Old 24-08-2014, 05:51   #17
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Re: Adding a 2nd AC input

Are you sure you are not just trying to draw >30A? You state that you have A/C, water heater, battery charger and reefer/freezer running off that circuit.

A 16kbtu A/C will draw 12-14A (much more on startup), the water heater will draw 12-14A, a 100A battery charger will draw 14-16A in bulk mode. I will assume the reefer/freezer is DC powered and isn't in play, but if not, it will draw 8-12A.

So is it possible that the breaker trips only when a certain combination of the above exceeds 30A? Just your A/C starting up with the water heater on is close to the breaker rating, and will trip if your breaker is a bit weak.

BTW, AC power doesn't work like described - the person closest to the box doesn't get to suck all the power from those further away, with the person on the end getting the dregs. If you are experiencing voltage sag, then the whole dock (circuit) is also. Assuming that the wiring is good, of course.

Mark
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Old 24-08-2014, 06:57   #18
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Re: Adding a 2nd AC input

As for how to measure current with a clamp on most techs have one or more break out cables.

These are short cable sets made from exposed conductors and a plug on one end and a socket on the other. I make mine from old power cords...

They permit the use of both a clamp on meter and a volt meter at the same time on each wire to measure both the current and the voltage drop as the current rises.

Another reason to consider having a pro do the work.


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Old 24-08-2014, 07:03   #19
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Re: Adding a 2nd AC input

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Originally Posted by colemj View Post
Are you sure you are not just trying to draw >30A? You state that you have A/C, water heater, battery charger and reefer/freezer running off that circuit.

A 16kbtu A/C will draw 12-14A (much more on startup), the water heater will draw 12-14A, a 100A battery charger will draw 14-16A in bulk mode. I will assume the reefer/freezer is DC powered and isn't in play, but if not, it will draw 8-12A.

So is it possible that the breaker trips only when a certain combination of the above exceeds 30A? Just your A/C starting up with the water heater on is close to the breaker rating, and will trip if your breaker is a bit weak.
Good point. That thought has been lurking in the back of my mind.

If this is the problem then it could be possible to avoid any modification to the OP's system by a little care in balancing the load. Example, turn off the water heater when using the air con and vice versa.
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Old 24-08-2014, 07:55   #20
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Re: Adding a 2nd AC input

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Originally Posted by Toubab View Post

I like the idea of having a second AC panel because, if I'm understanding everything correctly, if my air conditioning were to trip the breaker, I'd like to still have power to my refrigeration, batteries, etc. That's why I originally thought of adding a 2nd AC input.

That reminds me, our previous boat had twin 30-amp inlets. It also had a transfer bar on the distribution panel, so we could run the whole boat -- everything -- when we had both 30-amp shorepower cords on a dock pedestal. But we could also run some stuff -- most stuff, when it wasn't hot enough to need aircon -- with only one 30-amp supply.

We often used the single supply and the transfer bar during transits, partly 'cause it was easier, partly because we didn't often need much more than that.

Can't remember if others have mentioned it, but 50-amp 125/250V shorepower cable is heavy (about a pound/foot) and expensive.

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Old 24-08-2014, 08:43   #21
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Re: Adding a 2nd AC input

Quote:
Originally Posted by Fiveslide View Post
Since you ask this question I will assume you have triplex wire throughout the boat. You should be able to clamp onto the wires at the main breaker and the breaker for each circuit. They should be separated down to one wire at these locations. You can clamp on anywhere the outer covering has been removed exposing the white, black and green wire where you can get the clamp around the hot wire.

With all your stuff on and running, carefully clamp onto the wire at each breaker and see what amps are going through each circuit. Report your findings here.

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This... AND... Take a voltage reading at the same time...

Try a few different times of the day... ie different "dock loads"
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Old 31-08-2014, 11:54   #22
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Re: Adding a 2nd AC input

Quote:
Originally Posted by Fiveslide View Post
Since you ask this question I will assume you have triplex wire throughout the boat. You should be able to clamp onto the wires at the main breaker and the breaker for each circuit. They should be separated down to one wire at these locations. You can clamp on anywhere the outer covering has been removed exposing the white, black and green wire where you can get the clamp around the hot wire.

With all your stuff on and running, carefully clamp onto the wire at each breaker and see what amps are going through each circuit. Report your findings here.
I was able to peel back a little of the outer covering right behind the main inlet and get a reading. I drew about 20 amps when the air conditioning started up and then it quieted down to about 17-18 amps. So that should be a pretty accurate reading of what my whole system was drawing, correct? Now I should go and do the same thing just before the air conditioning breaker, and the refrigerator breaker, etc?

Quote:
Originally Posted by colemj View Post
Are you sure you are not just trying to draw >30A? You state that you have A/C, water heater, battery charger and reefer/freezer running off that circuit.

A 16kbtu A/C will draw 12-14A (much more on startup), the water heater will draw 12-14A, a 100A battery charger will draw 14-16A in bulk mode. I will assume the reefer/freezer is DC powered and isn't in play, but if not, it will draw 8-12A.

So is it possible that the breaker trips only when a certain combination of the above exceeds 30A? Just your A/C starting up with the water heater on is close to the breaker rating, and will trip if your breaker is a bit weak.
No, I'm not sure. Again that's part of why I wanted to add the second input. I have a 20 amp battery charger and an OLD 10 amp charger that I'm going to replace with a 60 amp charger as soon as I get all this figured out. The refrigeration is AC/DC so when AC power is available it uses that.

The reason I don't think that this is the issue is because it doesn't happen when the air con starts up (or at least that's not the only time it happens). Although with the measurements I just took, it looks like my air con draws almost as much power just to run as it does to start... so maybe.

Quote:
Originally Posted by colemj View Post
BTW, AC power doesn't work like described - the person closest to the box doesn't get to suck all the power from those further away, with the person on the end getting the dregs. If you are experiencing voltage sag, then the whole dock (circuit) is also. Assuming that the wiring is good, of course.

Mark
That's a big assumption at my marina lol. There's only one other person who lives aboard on my pier and I think he has 2 inputs like I'm talking about doing. I'll ask him if he's been having any trouble next time I see him. But isn't it true that no matter what, the longer your wire, the more voltage drop you're going to get? Or is that negligible when talking about 125V AC?

Thanks again everyone!
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Old 01-09-2014, 06:30   #23
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Re: Adding a 2nd AC input

Quote:
Originally Posted by Toubab View Post
I was able to peel back a little of the outer covering right behind the main inlet and get a reading. I drew about 20 amps when the air conditioning started up and then it quieted down to about 17-18 amps. So that should be a pretty accurate reading of what my whole system was drawing, correct? Now I should go and do the same thing just before the air conditioning breaker, and the refrigerator breaker, etc?
Have you replaced the main breaker? Did you have good voltage readings? Yes, I would test each circuit after testing the main breaker to be sure your reading actually includes all appliances. For example, your fridge may be switched on at your panel but not running because the thermostat cut it off, same with the water heater.



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Old 01-09-2014, 06:55   #24
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Re: Adding a 2nd AC input

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Originally Posted by Toubab View Post
I've been having problems with my main AC breaker tripping a lot. The best explanation I got was from a pro who said since I'm docked at the end of the pier, in the summer when lot's of people are running their air conditioning and dehumidifiers it puts a heavy load on the dock's wiring, causing a voltage drop and an amperage spike..................
A pro what? Basketball player?

Yes, the more current drawn through the dock's wiring the lower the voltage is apt to be but lowering the voltage does not increase the current. What you seem to be doing here is trying to figure out solutions to a problem you haven't identified yet. When a circuit breaker trips repeatedly, it's either because the current through the breaker is higher than the trip point or the circuit breaker is tripping at a current lower than it's supposed to trip at. So - before you cut holes in your boat or do something dangerous, find out why the breaker is tripping. You can either pay a pro to measure the current or you can buy a replacement breaker (with the same rating) and install it.

Anything else you do to the boat is going to be complicated, expensive, and out of your skill range (and probably your dad's as well).

It's possible to buy an isolation transformer with automatic voltage correction and install it on your boat or on the dock. While these are not inexpensive, this would probably a cheaper and better solution to your problem if the problem is caused by low or varying voltage at your dock pedestal.

Have you considered moving to a different slip? That's by far the simplest solution.
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Old 01-09-2014, 08:19   #25
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Re: Adding a 2nd AC input

For the motors in air conditioners lowering voltage does increase current.
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Old 01-09-2014, 15:26   #26
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Re: Adding a 2nd AC input

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For the motors in air conditioners lowering voltage does increase current.
Only if the load causes them to not run at their designed speed.

If the OP's breaker is tripping because his AC compressor is slowing down and drawing more current than it should, the circuit breaker is unknowingly protecting his compressor. Finding a solution to the breaker tripping problem without fixing the apparent low voltage problem could result in expensive air conditioner damage.
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Old 01-09-2014, 20:22   #27
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Re: Adding a 2nd AC input

One thing I have seen is AC compressors fail to start when voltage is low. If the breaker tripping can be correlated to when the thermostat turns the compressor on that would be a clue. Compressor stall can be due to lack of oil or incorrect gas charge.
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Old 02-09-2014, 07:39   #28
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Re: Adding a 2nd AC input

Hi

Just my two cents.

I experienced similar problems with my previous boat. The problem turned out to be that I had a short bw neutral and ground in my water heater and when and only when I was plugged to a dock which had GFCI I was tripping breakers when water heater thermostat was closing (turning on) without me drawing too much amps overall.

Michel


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Old 03-09-2014, 07:10   #29
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Re: Adding a 2nd AC input

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Originally Posted by goboatingnow View Post
surely if the problem is dockside voltage drop, adding a second feed wont really solve anything
In the OP situation it will help. A 30A load shared by two “feeds” each one protected by a 30A CB will most likely produce a 15A current per feed. 15A should not trip a 30A CB secondly the lesser current in the cords will make them more efficient.

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For the motors in air conditioners lowering voltage does increase current.
Correct, most induction machine will try to maintain there rated output. Lower voltage = higher current, higher voltage = lower current. When it involve large machine, it is common to adjust the voltage at the substation to obtain the machine rated current. For resistive load, Ohm’s Law apply.

In a normal situation the voltage at the power supply substation will be adjusted to provide the rated voltage to the middle of the load. Consumers the closer to the substation will experience higher voltage detrimental to appliances with more power for heating, consumers the further away from the substation will experience lower voltage also detrimental to appliances if it is for light globes lasting longer but less power for heating. There are some Standards to govern the supply of electricity, in some cases it is good to check if these Standards are respected.
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Old 03-09-2014, 08:56   #30
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Re: Adding a 2nd AC input

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Originally Posted by chala View Post
In the OP situation it will help. A 30A load shared by two “feeds” each one protected by a 30A CB will most likely produce a 15A current per feed. 15A should not trip a 30A CB secondly the lesser current in the cords will make them more efficient.
No in the USA you cannot use two different 30 amp lines together to boost the amps. US power the two 30 amp lines are out of phase and using two, depending on how you try it, will either cause a short or give the load double voltage and probably burn it out.
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