ABYC over current protection question

[Wdeertz]

I have my house bank in a 3x4 parallel configuration. (See attached diagram). The interconnecting cables for the top 2 rows of batteries is about 7-12 inches long (one bank required a longer wire to connect, compensated on the negative cable to keep resistance somewhat equal) and enclosed in a wire loom/sheath. From the 3rd row batteries to a 150A MBRF fuse the cable is 2 feet, also enclosed in a wire loom/sheath. From the bus bar to a 400A class T fuse are 2x 2/0 wires about 12 inches.

My question in looking at ABYC E-11, would the 150A MBRF fuse meet the 72 inch requirement? Total length from furthest battery to the MBRF fuse is about 48 inches. Even if I add in the additional 12 inches to the Class T fuse I’m still below 72 inches.

 

[READY]

I am no pro so this might not be helpful but it seems like for this setup you don't have any fuse that protects the wire runs that originate at the battery. You have big cables so they probably aren't at much risk. If you put the MRBF fuses on each battery that would perhaps be additional protection? Does the battery OEM specify a limit on qty of parallel batteries? 12 seems like a lot.

 

[Steve DAntonio]

Cables the originate at the battery and are sheathed can have OCP as much as 72" away, closer is always preferred. Wires that are are less than 7" long are exempt from OCP requirements.

The distance requirements, 72" for instance, is not collective. If I'm understanding your question, you are asking if collectively, these wire runs between batteries, are under 72" before OCP, are you compliant. The answer is no because there are 'new sources of power', each battery to which the wire is connected, which isolates the previous runs for OCP purposes.

Technically, if you have wire runs between batteries within a bank that are more than 7", from a positive terminal, they would need OCP, at both ends, which may be impractical unless you use the fuses that mount directly to the terminal. In the real world, wire runs between batteries, within a contiguous bank, typically aren't fused. Batteries that are part of the same bank electrically, but separated physically, a house bank that is connected to a thruster bank for instance, require OCP at both ends of the positive interconnecting cable.

My take on OCP https://stevedmarineconsulting.com/over-current-protection/

Here's the relevant standard...

11.10 OVERCURRENT PROTECTION
11.10.1 Overcurrent Protection - DC
11.10.1.1 GENERAL REQUIREMENTS
11.10.1.1.1 Overcurrent Protection Device Location - Ungrounded conductors shall be provided with overcurrent protection device(s) within a distance of seven inches (178 mm) of the point at which the conductor is connected to the source of power measured along the conductor (see FIGURE 8).
EXCEPTIONS:
1. Cranking motor conductors.
2. If the conductor is connected directly to the battery terminal and is contained throughout its entire distance in a sheath or enclosure such as a conduit, junction box, control box, or enclosed panel, the overcurrent protection shall be placed as close as practicable to the battery, but not to exceed 72 in (183 cm).
3. If the conductor is connected to a source of power other than a battery terminal and is contained throughout its entire distance in a sheath or enclosure such as a conduit, junction box, control box, or enclosed panel, the overcurrent protection shall be placed as close as practicable to the point of connection to the source of power, but not to exceed 40 in (102 cm).
4. Overcurrent protection is not required in conductors from self-limiting alternators with integral regulators if the conductor is less than 40 in (102 cm), is connected to a source of power other than the battery, and is contained throughout its entire distance in a sheath or enclosure.
5. Overcurrent protection is not required at an alternator if the ampacity of the conductor is equal to or greater than the rated output of the alternator.
6. Pigtails less than seven inches (178 mm) are exempt from overcurrent protection requirements.
NOTES:
1. Multiple main overcurrent protection devices may be connected to a common busbar connected directly to the source of power.
2. If the DC electrical distribution system is not connected as a grounded system per E-11.5.2.3, then both the positive and the negative DC conductors are ungrounded conductors.

And...

11.10.1.2 MAIN BATTERY OVERCURRENT PROTECTION
11.10.1.2.1 Overcurrent protection devices when installed as the main battery overcurrent protection device shall meet the requirements of E-11.10.1.6 or E-11.10.1.7.
11.10.1.2.2 For batteries or battery banks with a rating of 2200 CCA or 500 amp hours or less, battery overcurrent protection shall have a minimum ampere interrupting capacity (AIC) rating according to TABLE 3B.
11.10.1.2.3 For batteries or battery banks with a CCA rating greater than 2200 CCA or 500 amp hours, battery overcurrent protection shall have a minimum ampere interrupting capacity (AIC) rating as follows:
11.10.1.2.3.1 at least as great as the battery manufacturer’s short circuit rating, or
11.10.1.2.3.2 20 kA at 125 VDC or higher, if a battery manufacturer’s short circuit rating exceeds 10 kA.
NOTE: For batteries in series/parallel configurations the short circuit current of the battery bank is calculated by adding the short circuit current values of the batteries connected in parallel, and the short circuit rating of the batteries connected in series is not added for this calculation (e.g., six 6 VDC batteries are connected in series/parallel to create 12 VDC battery bank; if short circuit rating of a single battery equals 2400 A, the total calculated short circuit rating of the battery bank equals 7200 A).
11.10.1.2.4 Fuses, when used as main battery overcurrent protection, shall meet the ampere interrupting capacity (AIC) rating as stated in TABLE 3B.
EXCEPTION: Fuses less than or equal to 30 amps in 12 V systems, 15 amps in 24 V systems, and 12 amps in 32 V systems.

 

[Wdeertz]

Steve, as always thanks for your inputs. So if I understand your reply if I move the MBRF fuses to the 3rd row of batteries I’d be compliant as the interconnecting cables before this for each parallel bank are <=7 inches, is my understanding correct?

I’d put a MBRF fuse on each battery and fuse at 50 amps but space is at a premium and I’m not sure I have the space to do this.

 

[J.T kearney]

Mr. Wdeertz
What size amp hour are your batteries? I have 4 in parallel at 12 volts and 100 amp hours each. This is the maximum the manufacturer would allow. I fused each battery at the positive terminal with a MBRF, than cables to bus bar and then to a T fuse. Even though they each have a internal BMS, I worry that one might go sideways on me, so it would pop the fuse and I'd still have three working batteries.
Cheers J.T.

 

[Wdeertz]

Mr. Wdeertz
What size amp hour are your batteries? I have 4 in parallel at 12 volts and 100 amp hours each. This is the maximum the manufacturer would allow. I fused each battery at the positive terminal with a MBRF, than cables to bus bar and then to a T fuse. Even though they each have a internal BMS, I worry that one might go sideways on me, so it would pop the fuse and I'd still have three working batteries.
Cheers J.T.

24v@50Ahr so same energy content as 12v@100hr. Battleborn says unlimited parallel connections but I find this hyperbole. In any event 3 batteries in parallel shouldn’t be a problem. A MBRF fuse on each battery is ideal but not sure I have the space.

 

[Steve DAntonio]

Steve, as always thanks for your inputs. So if I understand your reply if I move the MBRF fuses to the 3rd row of batteries I’d be compliant as the interconnecting cables before this for each parallel bank are <=7 inches, is my understanding correct?

I’d put a MBRF fuse on each battery and fuse at 50 amps but space is at a premium and I’m not sure I have the space to do this.

In a word, yes, because those wires are over 7", installing the MBRF at those batteries would afford you compliant OCP protection. The wires that are under 7", within the bank, are exempt.

Make certain the fuses you use have the appropriate AIC, for the current produced by the aggregate batteries to which they are connected. Fault current can be 3-4 times CCA.

 

[Wdeertz]

Steve, I now remember why I put the Bluesea MBRF fuse on the bus bar rather than the 3rd row battery stud. The Bluesea MBRF fuse mounts on a 3/8” stud which is what the bus bar studs are. The Battleborn batteries come with 5/16” posts so putting the MBRF fuse on the battery stud would not provide a good connection. I’ve been unable to find a MBRF fuse which mounts on a 5/16” stud.

In any event, I’m still confused why if the interconnecting cables are <=7” putting the MBRF fuse on the bus bar with 24 inches of cable in wire loom would not meet the 72” exception.

 

[SteveK]

@SDA
In your link https://stevedmarineconsulting.com/over-current-protection/
I do not understand 7" OR 72" max and 7" OR 40" max

 

[Wdeertz]

@SDA
In your link https://stevedmarineconsulting.com/over-current-protection/
I do not understand 7" OR 72" max and 7" OR 40" max

As Steve is on the E-11 committee and is an expert on the subject he can explain better. Attached is an excerpt from the standard. As I understand it there is an exception to the 7” rule if the wire is in conduit, wire loom or otherwise protected. 72” if connected directly to the battery, the 40” has to do with a self limiting alternator or connected to other power source than a battery.

 

[SteveK]

@Wdeertz
Thanks for the explanation. All my cables are covered by a sheath, none are bare wires, so I guess within 72 inches is good enough.

 

[Fleming]

@Wdeertz
Thanks for the explanation. All my cables are covered by a sheath, none are bare wires, so I guess within 72 inches is good enough.

It sounds like you're calling the wire insulation a 'sheath'. It's not. In order to place the overcurrent protection more than 7" from the battery, and less than 72 inches, it needs to be in a split loom, coil loom, conduit, or even electrical tape spiral wrapped around the battery cable so that you have protection other than just the wire's insulation to prevent an accidental short.

Also, these aren't just ABYC recommendations. The 7", 40" 72" rule is also Federal law and covered under the USCG regulations.

 

[Stabi]

it needs to be in a split loom, coil loom, conduit, or even electrical tape spiral wrapped around the battery cable so that you have protection other than just the wire's insulation to prevent an accidental short.

I was under the impression that this meant conduit. So a Plastic split loom will also satisfy the regulations?

Thanks

 

[Fleming]

I was under the impression that this meant conduit. So a Plastic split loom will also satisfy the regulations?

Thanks

Yes, because the requirement is for a 'Sheath'. The following is in the ABYC standards in the USCG boat builders handbook section:

"2.4 SHEATH. Sheath means a material used as a continuous protective covering, such as electrical tape, molded rubber, molded plastic, or flexible tubing around one or more insulated conductors.

A “sheath” is a flexible continuous covering, as distinguished from a “conduit” or “duct” which are rigid continuous coverings. As the regulation states, a “sheath” may be a continuous wrapping of electrical tape, molded or extruded rubber or plastic, or flexible tubing (sometimes referred to as “spaghetti”).

A “sheath” may be used around one or a number of conductors, which may or may not be different gauges. Each of the conductors must be insulated, that is, the sheath is NOT to take the place of a conductor’s insulation."

 

[J.T kearney]

SteveD and Mr.Flemming
Thank you for all this info on marine electrical and wading through all the legalize. Where do I find table 3B referring to the AIC?. On my batteries I went up to a 125 amp fuse on each 100 amp Hr battery to avoid a nuisance tripping. I'm running 2/0 cable at all battery connections so not too worried about them. I wonder how many boats this forum has saved? I'm a big fan of fusing but do get misinformation.
Cheers
J.T.

 

[Fleming]

Here's the table. "See note 3" means a class T fuse.

 

[Comodave]

Steve, I now remember why I put the Bluesea MBRF fuse on the bus bar rather than the 3rd row battery stud. The Bluesea MBRF fuse mounts on a 3/8” stud which is what the bus bar studs are. The Battleborn batteries come with 5/16” posts so putting the MBRF fuse on the battery stud would not provide a good connection. I’ve been unable to find a MBRF fuse which mounts on a 5/16” stud.

In any event, I’m still confused why if the interconnecting cables are <=7” putting the MBRF fuse on the bus bar with 24 inches of cable in wire loom would not meet the 72” exception.

I have not checked lately but in the past I have bought them in a 5/16” hole size.

 

[J.T kearney]

Thank you Mr. Flemming for the quick response!!
Reading through table 3 on AIC do you think I'm on the right track going up on the fuse at the battery connection. 100 amp battery, 125 amp fuse?
Thank you all
J.T.

 

[SteveK]

Yes, because the requirement is for a 'Sheath'. The following is in the ABYC standards in the USCG boat builders handbook section:

"2.4 SHEATH. Sheath means a material used as a continuous protective covering, such as electrical tape, molded rubber, molded plastic, or flexible tubing around one or more insulated conductors.

A “sheath” is a flexible continuous covering, as distinguished from a “conduit” or “duct” which are rigid continuous coverings. As the regulation states, a “sheath” may be a continuous wrapping of electrical tape, molded or extruded rubber or plastic, or flexible tubing (sometimes referred to as “spaghetti”).

A “sheath” may be used around one or a number of conductors, which may or may not be different gauges. Each of the conductors must be insulated, that is, the sheath is NOT to take the place of a conductor’s insulation."

The english language continues to amaze me. The bolded and highlighted red does not exclude the 600* plastic covering of the wire as being a sheath.

What is the wire covering called?
At the most basic definition, wire insulation covers and holds wires together. It keeps the electrical current contained. Typically, wire insulation is made of different types of plastic or polymers, the two most common types being thermoplastic and thermoset.

 

[Steve DAntonio]

Steve, I now remember why I put the Bluesea MBRF fuse on the bus bar rather than the 3rd row battery stud. The Bluesea MBRF fuse mounts on a 3/8” stud which is what the bus bar studs are. The Battleborn batteries come with 5/16” posts so putting the MBRF fuse on the battery stud would not provide a good connection. I’ve been unable to find a MBRF fuse which mounts on a 5/16” stud.

In any event, I’m still confused why if the interconnecting cables are <=7” putting the MBRF fuse on the bus bar with 24 inches of cable in wire loom would not meet the 72” exception.

Bill, installing the fuses on the bus bar will meet the letter of the law if the wires leading to them are sheathed, however, they will provide absolutely no protection what so ever to those wires, which is the primary intent of the OCP. This is an issue I attempt to convey, sometimes successfully, to marine electricians in the field, particularly for OCP location. Just meeting the standard isn't always enough, the standard is the "floor", it's OK to exceed it and in the case of OCP it's important to remember why it's there, to protect the wires, so the closer it is to the source the better. I often see OCP installed 71 inches from a source, which can be compliant, and yet there's no reason why the OCP can't be closer, every inch of wire between the battery and the OCP is unprotected.

If these wires are sheathed and well-protected the need for OCP, beyond standards compliance, is pretty low, however, installing the fuses in your intended location will make no difference to them, they are simply compliance tools.

If you install the 3/8" MBRFs over 5/16" studs with 5/16" copper washers, I believe the resistance would be negligible. The stud is primarily used to maintain compressive contact between the base of the MBRF, and terminal area directly beneath the stud.

Does that make sense?

 

[Steve DAntonio]

@SDA
In your link https://stevedmarineconsulting.com/over-current-protection/
I do not understand 7" OR 72" max and 7" OR 40" max

Steve:

This detail confuses many professionals. The diagram included in the article spells this out, however, in simple terms it is as follows.

OCP is required within 7" of every positive battery terminal, with the exception of starter cables, which are exempt.

That distance may be extended to 72" if the wire is supplementally sheathed, and that sheathing could be as simple as electrical tape, or it can be a conduit. Typically, purpose made, fire retardant (it has a blue stripe on it) split loom is used for this purpose. It may NOT be spiral wrap loom.

OCP is required within 7" of any secondary source of power such as a battery switch, bus bar or starter positive post. That distance may be extended to 40" of the wire is sheathed.

Does that make sense?

In Munich, bound for Ancona, Italy for sea trials.

 

[Steve DAntonio]

It sounds like you're calling the wire insulation a 'sheath'. It's not. In order to place the overcurrent protection more than 7" from the battery, and less than 72 inches, it needs to be in a split loom, coil loom, conduit, or even electrical tape spiral wrapped around the battery cable so that you have protection other than just the wire's insulation to prevent an accidental short.

Also, these aren't just ABYC recommendations. The 7", 40" 72" rule is also Federal law and covered under the USCG regulations.

Covered by the Fed Law/CFR only for gasoline powered vessels. In the US, recreational, diesel-powered vessels under 65 feet are covered by no law as far as systems such as electrical, fuel, propulsion etc., save nav lights, horn, PFDs etc.

Discontinuous spiral wrap, or "coil loom" lacks ABYC compliance.

 

[Wdeertz]

Bill, installing the fuses on the bus bar will meet the letter of the law if the wires leading to them are sheathed, however, they will provide absolutely no protection what so ever to those wires, which is the primary intent of the OCP. This is an issue I attempt to convey, sometimes successfully, to marine electricians in the field, particularly for OCP location. Just meeting the standard isn't always enough, the standard is the "floor", it's OK to exceed it and in the case of OCP it's important to remember why it's there, to protect the wires, so the closer it is to the source the better. I often see OCP installed 71 inches from a source, which can be compliant, and yet there's no reason why the OCP can't be closer, every inch of wire between the battery and the OCP is unprotected.

If these wires are sheathed and well-protected the need for OCP, beyond standards compliance, is pretty low, however, installing the fuses in your intended location will make no difference to them, they are simply compliance tools.

If you install the 3/8" MBRFs over 5/16" studs with 5/16" copper washers, I believe the resistance would be negligible. The stud is primarily used to maintain compressive contact between the base of the MBRF, and terminal area directly beneath the stud.

Does that make sense?

Steve, thanks, makes perfect sense.

 

[SteveK]

Steve:

This detail confuses many professionals. The diagram included in the article spells this out, however, in simple terms it is as follows.

OCP is required within 7" of every positive battery terminal, with the exception of starter cables, which are exempt.

That distance may be extended to 72" if the wire is supplementally sheathed, and that sheathing could be as simple as electrical tape, or it can be a conduit. Typically, purpose made, fire retardant (it has a blue stripe on it) split loom is used for this purpose. It may NOT be spiral wrap loom.

OCP is required within 7" of any secondary source of power such as a battery switch, bus bar or starter positive post. That distance may be extended to 40" of the wire is sheathed.

Does that make sense?

In Munich, bound for Ancona, Italy for sea trials.

Your explanations always put it into perspective of the intent of ABYC.
The bolded orange needs more clarity. If a starter cable is exempt why does OCP need to be 7" from starter post, did you mean alternator?

 

[Bmarler]

Your explanations always put it into perspective of the intent of ABYC.
The bolded orange needs more clarity. If a starter cable is exempt why does OCP need to be 7" from starter post, did you mean alternator?

pretty sure that means a power take off from the starter post. many times the starter post is a more convenient place to grab power.

 

[J.T kearney]

Hi
Is the clearance on the top of your batteries that's giving you trouble using MRBF on your battery post?. There might be solutions from someone on the forum.
Cheers J.T.

 

[SteveK]

pretty sure that means a power take off from the starter post. many times the starter post is a more convenient place to grab power.

I suppose the OCP exempt status of a starter cable ends at the starter post, but then would a sheating not be required up to the starter post.

 

[Steve DAntonio]

pretty sure that means a power take off from the starter post. many times the starter post is a more convenient place to grab power.

Exactly, it's a secondary distribution point, like a bus bar.

In Ancona, Italy, preparing for sea trials.

 

[tiltrider1]

Exactly, it's a secondary distribution point, like a bus bar.

In Ancona, Italy, preparing for sea trials.

You should ask if the snails are in season. An excellent local dish in Ancona.

 

[Steve DAntonio]

Ha, thanks, they aren't, but so much else is;-)