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**knottybuoyz** · 04-11-2006, 15:35

I have to rewire the AC system, 120V 30 Amp, on the ole boat in the spring. It was originally wired with 14/3 house wire and that's definitely gotta go. All the branch circuits are 14/2 house and that's not right either. I've been flipping through ABYC E-11 for conductor sizes and there's no mention of what's required. So I guess my question is what size wire is required? 14/3 ok or should I go to 12/3? Heavier?

**GordMay** · 04-11-2006, 16:13

14/2 + Gnd.* is suitable for 15A 120VAC circuits.
#12 is rated 20A, and #10 is rated 30A.

*2 conductors plus ground.

**knottybuoyz** · 04-11-2006, 17:13

Thanks Gord

Wire's ordered.

Who's got he best price (online) for the Ancor Automatic wire stripper P/N 702030 and the Double Crimp Ratchet tool P/N 701030? Can't seem to locate a local Cdn supplier.

RandyAbernethy · 04-11-2006, 18:15

Gord: My ABYC chart says 12 AWG Boat Cable is good for 45 amps outside the engine room and 38.3 inside. I also read 14 AWG good for 35 amps outside the engine room. Over sizing for safety margin, or am I missing something (or both...)?

Rick · 04-11-2006, 20:55

In general, the higher the temperature rating of the jacket material the higher the current rating of the conductor, up to a point.

Aside from the fact that one can obtain 12/3 wire rated at over 20 Amps I would not use even a 14/3 rated at 15 Amps to power a microwave or especially a space heater rated at 1200 to 1500 Watts and here's why. If you "dedicate" a particular duplex outlet (use a 20 A rated one for heater and microwave oven plug-ins) then the cyclical copper heating at the plug/receptical interface will take much longer to degrade than when "pushing" the outlet and wire ratings to their limit. What happens when you use a space heater for a few years worth of "winter" is that you need to access the wire connections and tighten them due to the annealing of the copper caused by the copper loss heating at or near 15A of long use. If you don't then you will feel the warmth of the plug when the heater (or microwave) has been on for several minutes. This does not bode well over time for safety on a boat, in my opinion.

The price and weight differential between 14/3 and 12/3 wires and for 20 A rated recepticals "dedicated" to the branch circuits where you know where heavy loads will be plugged into just isn't worth it compared to the inherently safer cool running installation hidden from view. Keep in mind that just because you have a 20A rated wire and receptical doesn't mean that you cannot install a 15A breaker for that branch, you can and perhaps should.

Be safer instead of a sorry worrier.

**GordMay** · 05-11-2006, 01:54

The first outlet, in each 120VAC circuit, should be a ground-fault (GFCI) receptacle.

Quote:

Originally Posted by RandyAbernethy

Gord: My ABYC chart says 12 AWG Boat Cable is good for 45 amps outside the engine room and 38.3 inside. I also read 14 AWG good for 35 amps outside the engine room. Over sizing for safety margin, or am I missing something (or both...)?

Indeed, ABYC does permit higher amperages, than those I cited - which are from the NEC & CEC*.
I have never been satisfied with the ampacities ABYC permits (nor the minimum 16 gauge wire permitted) , and remembering that "Standards & Codes" generally specify minimums, I use the higher criterion set by the land-based authorities.
I should have also noted that circuits should generally be loaded to not more than 80% of their rated capacity, hence:
- a 15 A Breaker, protecting #14 AWG wire should have a maximum connected load of 1500 Watts, or 15.5 Amps, or less. (In much larger sizes, there are 100% rated breakers).

*National Electrical Code (NFPA 70) & Canadian Electrical Code

Quote:

Originally Posted by Rick

In general, the higher the temperature rating of the jacket material the higher the current rating of the conductor, up to a point ...

... The price and weight differential between 14/3 and 12/3 wires and for 20 A rated receptacles "dedicated" to the branch circuits where you know where heavy loads will be plugged into just isn't worth it compared to the inherently safer cool running installation hidden from view. Keep in mind that just because you have a 20A rated wire and receptacle doesn't mean that you cannot install a 15A breaker for that branch, you can and perhaps should ...

The greatest risk for overheating of minimally-sized (minimally legal) wiring is on electric Heating & Air-Conditioning circuits, which often remain continually energized. Other higher-amperage circuits, such as Microwaves & Hot Water Heaters tend to cycle “off” often enough to mitigate this phenomena.

The combination 15 & 20A** receptacles are designated NEMA “5-20R”, or CSA “5-20RA” in Canada .

** wherein the larger (white/neutral) slot is “T” shaped, to accept both 15 and 20A Male Plugs.

Marinco® has an excellent publication: “Boater’s Guide to AC Electrical Systems” at:
http://www.marinco.com/corp/how_to_guides.html

The Paneltronics Technical Section offers:
“Excerpts ABYC E-11"
At: http://www.paneltronics.com/technica...nicalCover.htm

Also Contact:
ANCOR Marine Grade™ Products (800) 424-WIRE
Tel: (707) 792-0312
Fax: (707) 795-7950
E-mail: marketing@ancorproducts.com
and ask for their publication:
”A complete marine electrical system reference guide”

See also my tutorial “Ohm’s Law & Boats” (dealing /w Voltage Drop) at: http://www.cruisersforum.com/forums/...read.php?t=372
andhttp://www.cruisersforum.com/gallery...age.php?i=1316

**knottybuoyz** · 05-11-2006, 08:26

I think I'm going to be Ok with what I've ordered. The largest AC load is the battery charger @20A . I bought 10/3 to feed the AC side of the panel from the shorepower inlet and will run the 10/3 back to the charger. We don't have a microwave or other high AC loads so all the feeder circuits will be run with 12/3.

We use a Xantrex 750+ inverter to run the fridge and laptop while underway. What I'd like to do is wire the AC output from the inverter into the panel for onboard distribution of AC while underway. I'm not sure of the safest way to do this. I'm more concerned with switching from shorepower to inverter. I'm assuming without a switch in the system somewhere I'll have to ensure the inverter is turned off while on shorepower and only switching it on when the shorepower is disconnected. Unless there's another way that any of you know of I'd appreciate hearing about it.

btrayfors · 05-11-2006, 09:26

Rick,

One way to do this is to use breaker/toggle units designed to select one or another (not both) AC sources. And example would be the Blue Seas 8032: http://www.starmarinedepot.com/Blue+...+Selector.html

I have two of these on my boat which has two 30-amp shore circuits. I use them to choose either AC shore power or the AC generator as sources to feed my onboard circuits. You could easily use the same technique to choose either AC shore power OR AC from the inverter.

These switches have a slide which prevents both sources from being selected at the same time: you select EITHER one source OR the other.

They're simple, relatively inexpensive, and work great.

Bill

RandyAbernethy · 05-11-2006, 09:30

Great info, thanks Gord & Rick (Seattle type). Good luck with the new AC lines Rick (Canada type).

coot · 07-11-2006, 17:55

Quote:

Originally Posted by knottybuoyz

We use a Xantrex 750+ inverter to run the fridge and laptop while underway. What I'd like to do is wire the AC output from the inverter into the panel for onboard distribution of AC while underway. I'm not sure of the safest way to do this. I'm more concerned with switching from shorepower to inverter. I'm assuming without a switch in the system somewhere I'll have to ensure the inverter is turned off while on shorepower and only switching it on when the shorepower is disconnected. Unless there's another way that any of you know of I'd appreciate hearing about it.

I switch my inverter into the 15 A branch circuits instead of the 30 A shore power feeds. I used 20 A DPDT toggle switches, which is ok because the 20 A rating of the switch is greater than the 15 A circuit. I switch both legs of the AC circuit and have all the grounds wired together.

So I have 5 branch circuits on board, but only 2 of them can be connected to the inverter. But those two are the branches that feed the electrical outlets and the microwave oven, so I'm fine. I do not mind that the inverter cannot be used to power the battery charger.

The principal advantage I see is that no truly bad configurations are possible with any switch settings. I can never run the battery charger off the inverter; I can never run the air conditioner off the inverter, etc. I also can never connect two AC sources to the same circuit. A nice bonus is that the cost of 2 of the 20 A DPDT switches is substantially less than a single 30 A transfer switch, and the switches themselves are much smaller.

**knottybuoyz** · 07-11-2006, 18:46

Great Idea Coot! Thanks. I think that'll work nicely!

I was balking at the price of the price of the x-fer switch as well as I have no place to mount it. There's 4 empty slots in the panel so I can work around the space limitation.

Thanks again. Now just have to wait till spring to get started on the re-wiring.

Rick

delmarrey · 08-11-2006, 20:43

Theses?

http://www.ancorproducts.com/whats_n.../homepage.html

**knottybuoyz** · 09-11-2006, 04:55

Quote:

Originally Posted by delmarrey

Theses?

Yup! That's them Del. Although I missed that particular set of tools. I've asked the Admiral to get me them for X-mas. She just got a raise so it shouldn't be an issue. We'll have to import from the US as most marine suppliers up here haven't got a clue what I'm talking about or they want a rediculous amount of money (like 3X the US retail price) for them.

Ordered the wire from (www.bestboatwire.com) and got a great deal on some "end-of-roll" stock. Saved about half off of retail.

Thanx again.

Rick