ABYC Inverter Circuit Protection

Kevin,

Could you please clarify the ABYC recommendation (and Reference Code) for the need for over-current protection at BOTH ends of a conductor (e.g., #10 AWG), or just at end where overload may originate?ABYC-logo

Thanks.

Hi,

The only time that I am aware of circuit protection at both ends of a conductor are on charging circuits where the charger is not self-limiting.

Most battery chargers and alternators are self limiting so your circuit protection is only required at the connection to the DC system.

Hope this helps,

Kevin

Hi Kevin,

Thanks for your reply.

Because I wasn’t very clear in my previous message, my inquiry relates to the AC wiring, not DC wiring, on my 53′ Hatteras FBMY.

Let me be specific, if I may….I’ve been informed from a survey that I need to install a 30 amp circuit breaker on the “AC output from” and “AC feed into” the Inverter/Charger (each a separate #10 AWG color-coded wire, as installed by the technician) on my boat.

My question is…does ABYC recommend/specify a circuit breaker at both ends, or just one end, namely, ” just at end where overload may originate”?

I’m most interested in doing things the right way. I look forward to your advice.

Regards.

Hi,

If the inverter is not self limiting, then circuit protection is required on both ends.

Here is a quote from ABYC

11.10.2.8 Location of Overcurrent Protection – AC Circuits

11.10.2.8.1

Each ungrounded current carrying conductor shall be protected by a circuit breaker or fuse.

11.10.2.8.1.1

A circuit breaker or fuse shall be placed at the source of power for each circuit or conductor except that

11.10.2.8.1.2

if it is physically impractical to place the circuit breaker or fuse at the source of power, it can be placed within seven inches (178 mm) of the source of power for each circuit or conductor, measured along the conductor.

11.10.2.8.1.3

if it is physically impractical to place the circuit breaker or fuse at or within seven inches of the source of power, it can be placed within 40 inches (102 cm) of the source of power for each circuit or conductor, measured along the conductor, if the conductor is contained throughout its entire distance between the source of power and the required circuit breaker or fuse in a sheath or enclosure such as a junction box, control box, or enclosed panel.

Since the AC out of the inverter is considered a source of power, per 11.10.2.8.1.1, it should have a breaker.

Hope this helps

Kevin

Hello Kevin:

Thanks for getting me the ABYC quote. Since ABYC specifies the following, I will give my interpretation of what I need to do and ask for your comments (please see below).

11.10.2.8 Location of Overcurrent Protection – AC Circuits

11.10.2.8.1
Each ungrounded current carrying conductor shall be protected by a circuit breaker or fuse.

11.10.2.8.1.1
A circuit breaker or fuse shall be placed at the source of power for each circuit or conductor except that

11.10.2.8.1.2
if it is physically impractical to place the circuit breaker or fuse at the source of power, it can be placed within seven inches (178 mm) of the source of power for each circuit or conductor, measured along the conductor.

Now to my specific situation…there is a 4-Conductor #10 AWG Mulitcable connection (therefore the need for a 30 amp circuit breaker) between the Inverter/Charger and the boat’s AC PANEL, with the RED conductor as the AC HOT IN, and a GREEN conductor as the NEUTRAL IN. In addition, there is a BLACK conductor as the AC HOT OUT and a WHITE conductor as the NEUTRAL OUT from the Inverter/Charger (see attached sketch).

As I interpret the ABYC information, I should install a 30 amp breaker at no more than 7 inches of the INVERTER AC TERMINAL BLOCK between the AC HOT OUT terminal (i.e., “the source of power”) and the BLACK conductor as it continues to the AC PANEL (see attached sketch).

Similarly, should I install a 30 amp breaker at the AC PANEL at no more than 7 inches between the SHORE POWER AC HOT (i.e., “the source of power”) and the RED conductor as it continues to the INVERTER AC TERMINAL BLOCK (see attached sketch)?

As such, I interpret that neither of the NEUTRAL conductors needs any over current protection. Does this mesh with your thinking?

I certainly appreciate your assistance!

Hi Nick,

Your breaker locations are correct.

Dual pole breakers are used when you are not positive which wire AC wire is truly the HOT. Beyond the reverse polarity light, only the black, AC hot, is broken by the breaker. If the inverter is connected to the AC system after the dual pole main, then only a single pole breaker is required.

It is common practice have a dual pole breaker on the output side of generators and inverters even though in my opinion they are not necessary. The neutral is connected to the case ground to ensure which side of the AC output is really hot.

Hope this helps,

Kevin