Adding shore power

J

jdavis

Advanced Member
Joined
Jan 28, 2022
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Hello! My FWC Hawk is supposed to be built and delivered next month. It is the shell model with a furnace only. I would like to add shore power and use a LiFePO4 battery. Could yall take a look at my diagram and let me know if it should work? Thanks a lot! This forum has been a great resource.

Camper Power.jpeg
 
I would put a fuse or circuit breaker as close to the battery as possible, minimizing the amount of unfused wire.

If I had to choose only one charging source, I’d probably choose a dc to dc charger from the truck system. Care to share your thinking behind going shore power only?
 
First, welcome to Wander The West! We have great folks to hang out with, here on the web. Please post some photos when you get your camper.

My only thought… Is there (should there be) a cktbkr between the power inlet and the converter?
 
Wandering Sagebrush,

While what you are suggesting wouldn’t hurt, I think that what he has in his drawing would be considered acceptable. The idea of the related codes is that the connector type is only to be installed on a 30 amp cord, which is only to have a 30 amp specific connector on the other end so it can only be connected to a 30 amp circuit receptacle. By sizing the wire in the camper from the external connector to the first circuit breaker panel for 30 amps, that wire is adequately protected by the circuit breaker that protects the shore power circuit.
 
Jon R, the main reasons I left out the truck alternator was complexity and I just don't think I need it. I have shore power about 95% of the time. It may be way less complex than the impression I got from my initial research.

Jon R thats a great point about the breaker. Would you suggest moving the breaker from between the bus bar and DC distribution panel to between the battery and bus bar? Thanks for looking!

Wandering Sagebrush, thank you for the warm welcome! The Blue Sea Systems 1214 has two breaker protected 15 amp circuits. The charger/converter would be on one of those 15 amp breaker protected circuits. 15 amp breaker doesn't seem ideal to me, since the converter should only be using about 5 to 6 amps, but I could not find a smaller breaker.
 
When deciding where fuse/cb protection should go and what its trip level should be, imagine shorts to ground in each of the wire run sections and think of where the fault current can come from (keep in mind it may come from multiple sources - a battery to battery wire should be fused at both ends for example). Each section of wire should be protected by a fuse that is sized to protect the size wire that was used.

The fuse at the battery should be sized to protect the smallest wire it supplies unless that smaller wire is protected by its own smaller fuse. So the answer to your question about moving the 30 amp fuse would depend on your wire gage. If all of your wire is 10 awg, moving the 30 amp fuse to near the battery would be ok. I’m assuming your dc converter output is internally fused or current limited. If so, the circuit breaker you put at its output is not necessary to protect the wire, but may be an advantage for fault detection.
 
jdavis said:
... The charger/converter would be on one of those 15 amp breaker protected circuits. 15 amp breaker doesn't seem ideal to me, since the converter should only be using about 5 to 6 amps, but I could not find a smaller breaker.
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That should be ok. A basic principle of electrical system design is that the circuit protection is intended to protect the wiring, and supplied equipment has its own protection, and does not rely on the power supply system for protection. As long as the wire to the charger is adequately protected by the circuit breaker you are following industry practice.
 
Jon R said:
That should be ok. A basic principle of electrical system design is that the circuit protection is intended to protect the wiring, and supplied equipment has its own protection, and does not rely on the power supply system for protection. As long as the wire to the charger is adequately protected by the circuit breaker you are following industry practice.
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That's a great point. Thanks!
 
Jon R said:
Wandering Sagebrush,

While what you are suggesting wouldn’t hurt, I think that what he has in his drawing would be considered acceptable. The idea of the related codes is that the connector type is only to be installed on a 30 amp cord, which is only to have a 30 amp specific connector on the other end so it can only be connected to a 30 amp circuit receptacle. By sizing the wire in the camper from the external connector to the first circuit breaker panel for 30 amps, that wire is adequately protected by the circuit breaker that protects the shore power circuit.
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From a brief conversation with Marty @ATC, I was under the impression that an external CB was required. If the CB in the converter meets standards, all is well.
 
The cb or other protection in the converter should prevent an unsafe condition within the converter itself and provide protection for properly sized wire downstream of the converter. In the OP’s design the 120 VAC circuit breakers protect the wire downstream of those breakers. What is left unprotected by the camper equipment is the wire from the shore power connector to that first 120 VAC breaker. That is the same way our campers are wired from the factory as far as I know. I see nothing in the literature about a fuse or cb right at the shore power connector. That wire run is typically short - less than 3 feet in my camper. I believe that lack of a protection device for that short run is common, and is allowed as long as the camper wire in the section from the shore power connector to the first circuit protective device is sized to match the rated capacity of the external connector.

It is possible for someone to defeat that scheme by making a nonstandard cable and connecting to a 60 amp supply, for example, but the assumption is people will follow the codes. RV parks are notorious for having wiring issues, though, so it pays to examine the supply setup if you are connecting away from home. Many people recommend a combination surge suppressor and appropriately rated circuit protective device be used in line if you connect at an RV park to ensure even the entry wiring of your camper is properly protected.
 
I would consider moving the 30A breaker between the buss bar and the fuse block to be between the battery and the buss bar. I'm in the camp of having some sort of protection as close to the battery as possible, putting the fuse or breaker between the battery and everything else. Depending on the number of your connections the out terminal of the break can be your buss bar.
 
ntsqd said:
I would consider moving the 30A breaker between the buss bar and the fuse block to be between the battery and the buss bar. I'm in the camp of having some sort of protection as close to the battery as possible, putting the fuse or breaker between the battery and everything else. Depending on the number of your connections the out terminal of the break can be your buss bar.
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Thanks, that's a great suggestion.
 
Based on the input I received here and another forum I have made some updates. Most notable are going with bigger battery and charger, and adding an EMS on the AC power in side. Thanks everyone for the feedback!

Camper Power.v3.jpg
 
What will the total length of the battery charging circuit be? Same for the battery to fuse block circuit length? 6 ga. seems rather large even with keeping the voltage drop to a minimum. I ran 6 ga. for the truck to camper charging circuit to keep the voltage drop less than 3% at an estimated 20A charge with a max of 80 amps, but the total length of the circuit is about 25 feet.
 
All the runs should be less than 3 feet. I went with 6 because the charger is rated at 45 amp output. The Blue Sea chart I looked at listed 8 awg good for 40 amps and 6 awg good for 50 amps.
 
That's pretty confusing. We are talking 10ga to 6ga. I think I trust the ABYC more, but maybe I'll split the difference and use 8ga.
 
The length of the circuit is a huge factor with low voltage. If you work the calculator or set up the formula in a spreadsheet it's pretty easy to see this.

The NEC doesn't worry too much about circuit length in residential or industrial circuits, but then it is constructed so that the wires are sized such that the circuit length isn't a factor and those electricians don't have to do that math. They're also working with 10 times the voltage, which makes a difference too.
 
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