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Old 10-20-2020, 08:55 AM   #1
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Relocating Water Heater - Wire Extension

I am relocating my water heater. In addition to a circuit breaker, the heater is presently wired through an on-off switch in the engine room. My questions are:

1) Should I retain the switch and run a new wire from the switch to the heater?
2) Or, should (could I, safely) eliminate the switch by butt-splicing into the existing run?

In any case, I plan on using 10-gauge tinned three-conductor boat wire to lessen resistance as the run will be extended by about fifteen feet.
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Old 10-20-2020, 09:55 AM   #2
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While boats often break some of the NEC rules for home wiring, any splice should be in a junction box. So why not use the switch?

10 gauge would be rather healthy. 14 gauge would meet code if the circuit has a 15 amp breaker. 1 volt of drop is a lot for a 12V circuit, but peanuts for a 110V AC circuit.

David
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Old 10-20-2020, 10:31 AM   #3
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You didn't specify whether 120 or 240 VAC and the wattage of the element. Assuming 120 VAC 1,500 watts, you can't go below 10 gauge as you're adding 15' and that's reaching the limit of 10 gauge before you add the existing distance. IMO, run new and eliminate the added resistance in the splice or switch. If you don't need the switch, best to eliminate it.

Ted
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Old 10-20-2020, 11:15 AM   #4
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I don't understand. You can run 14 gauge wire 50' (in one direction) as is done in most all houses, and keep the voltage drop down to less than 3%. 100' if it is 220V. AC is a different animal than DC.

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Old 10-20-2020, 12:15 PM   #5
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I'd keep the switch if it's near the water heater. If not, I'd lose the switch and butt-splice in a junction box. David is correct - assuming 1500-watts of heater, 10ga wire is over-kill. 14-ga is code for 15A circuits (1800w); 12-ga is code for 20A circuits (2400w). I don't remember how big 10A goes, but it's what I ran for a 240v pool pump recently.

The reason I like a switch near a water heater is if the water heater is empty and you flip the breaker, you will burn-out the heating elements in a few seconds. Typically, the water heater is only empty for winterizing or swap-out. With the switch right there, you can manually disconnect and not forget later. It also may be a building code item to have a switch right there, but not positive.

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Old 10-20-2020, 01:55 PM   #6
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Originally Posted by mvweebles View Post
I'd keep the switch if it's near the water heater. If not, I'd lose the switch and butt-splice in a junction box. David is correct - assuming 1500-watts of heater, 10ga wire is over-kill. 14-ga is code for 15A circuits (1800w); 12-ga is code for 20A circuits (2400w). I don't remember how big 10A goes, but it's what I ran for a 240v pool pump recently.

The reason I like a switch near a water heater is if the water heater is empty and you flip the breaker, you will burn-out the heating elements in a few seconds. Typically, the water heater is only empty for winterizing or swap-out. With the switch right there, you can manually disconnect and not forget later. It also may be a building code item to have a switch right there, but not positive.

Peter
10 gauge is good up to 30 amps. Keep the switch or not is up to your preference. As to burning out the element I used to believe that but back in 2001 we bought a boat. It had been sitting tied to the dock for a couple of years. I was in the engine room and heard a sizzling sound. Found it to be the water heater being empty and turned on. Turned it off and assumed that I would be replacing the element. However I owned that boat for 8 years and the element worked perfectly after being turned on for at least 2 years and the tank empty. So now either I had a super element or they donít always burn out...
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Old 10-20-2020, 02:02 PM   #7
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My Isotherm has an internal element over heat trip to keep it from burning out from no water.
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Old 10-20-2020, 03:33 PM   #8
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Thanks guys for your advice. I have decided to eliminate the switch. It will be nowhere near the new location plus the switch adds another point of resistance albeit not much but one less point of failure in any case. As usual, no one correct answer. There are few in the boating world. The new location will be under the master stateroom bed platform and will be moderately easy to access through a large hatch under the mattress should I ever have a problem. The hot and cold water supply will have shut-offs in the engine, the former location. Big space saver.
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Old 10-20-2020, 04:41 PM   #9
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I have a relay with a 12v coil to turn my heater off and a switch in the galley so I don't have to go to the ER every time.
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Old 10-20-2020, 05:19 PM   #10
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If the new location is so far away from the current location then I would just put in a new run from the electrical panel to the new location. Then you donít have any splices. I just use the circuit breaker as a switch for the water heater. It is out in the salon so it is very convenient.
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Old 10-20-2020, 05:22 PM   #11
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Quote:
Originally Posted by DavidM View Post
I don't understand. You can run 14 gauge wire 50' (in one direction) as is done in most all houses, and keep the voltage drop down to less than 3%. 100' if it is 220V. AC is a different animal than DC.

David
Quote:
Originally Posted by mvweebles View Post
I'd keep the switch if it's near the water heater. If not, I'd lose the switch and butt-splice in a junction box. David is correct - assuming 1500-watts of heater, 10ga wire is over-kill. 14-ga is code for 15A circuits (1800w); 12-ga is code for 20A circuits (2400w). I don't remember how big 10A goes, but it's what I ran for a 240v pool pump recently.

The reason I like a switch near a water heater is if the water heater is empty and you flip the breaker, you will burn-out the heating elements in a few seconds. Typically, the water heater is only empty for winterizing or swap-out. With the switch right there, you can manually disconnect and not forget later. It also may be a building code item to have a switch right there, but not positive.

Peter
Regarding wire size:

14 gauge has a length limit relative to amperage. Depending on the wire it also has a temperature limit for the amperage. The limits also consider whether a single cable or a bundle of cables in a conduit or other confined space that limits heat dissipation.

In my calculation, I considered it passing through an engine room (120 degree temperature), incorporated in a bundle of wires and certainly wouldn't design a circuit with a 3% voltage drop in a marine environment.

Further, house wiring is designed with an unlimited source of power other than the circuit breakers. Being on a boat with a much more limited amount of power (on the generator), it's conceivable that there is already 3% or move voltage loss between the generator and breaker panel when the generator is seeing 75% load before the water heater.

Finally, without knowing the length of the run from the generator to the breaker panel and the existing run to the switch, it would be difficult to justify reducing the wire by 2 sizes while increasing length by 15'. If the current wire is original, clearly the boat manufacturer had a reason for spending modestly more on increased wire size.

Ted
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Old 10-20-2020, 05:30 PM   #12
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Originally Posted by O C Diver View Post
Regarding wire size:

14 gauge has a length limit relative to amperage. Depending on the wire it also has a temperature limit for the amperage. The limits also consider whether a single cable or a bundle of cables in a conduit or other confined space that limits heat dissipation.

In my calculation, I considered it passing through an engine room (120 degree temperature), incorporated in a bundle of wires and certainly wouldn't design a circuit with a 3% voltage drop in a marine environment.

Further, house wiring is designed with an unlimited source of power other than the circuit breakers. Being on a boat with a much more limited amount of power (on the generator), it's conceivable that there is already 3% or move voltage loss between the generator and breaker panel when the generator is seeing 75% load before the water heater.

Finally, without knowing the length of the run from the generator to the breaker panel and the existing run to the switch, it would be difficult to justify reducing the wire by 2 sizes while increasing length by 15'. If the current wire is original, clearly the boat manufacturer had a reason for spending modestly more on increased wire size.

Ted
+1
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Old 10-20-2020, 05:37 PM   #13
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Quote:
Originally Posted by O C Diver View Post
Regarding wire size:

14 gauge has a length limit relative to amperage. Depending on the wire it also has a temperature limit for the amperage. The limits also consider whether a single cable or a bundle of cables in a conduit or other confined space that limits heat dissipation.

In my calculation, I considered it passing through an engine room (120 degree temperature), incorporated in a bundle of wires and certainly wouldn't design a circuit with a 3% voltage drop in a marine environment.

Further, house wiring is designed with an unlimited source of power other than the circuit breakers. Being on a boat with a much more limited amount of power (on the generator), it's conceivable that there is already 3% or move voltage loss between the generator and breaker panel when the generator is seeing 75% load before the water heater.

Finally, without knowing the length of the run from the generator to the breaker panel and the existing run to the switch, it would be difficult to justify reducing the wire by 2 sizes while increasing length by 15'. If the current wire is original, clearly the boat manufacturer had a reason for spending modestly more on increased wire size.

Ted

+2. I always run wire that is at least 1 size larger than required. It is a small 1 time cost and things run better with good voltage.
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Old 10-21-2020, 05:29 AM   #14
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I have always found that "overkill" on wiring sizes is a non issue,

Sure if it was a racing boat you might not like the added weight , but for a cruiser its a non issue.

10 Ga suits almost every load most cruisers are likely to require , since wire is cheapest in a factory coil , 100 or 250 ft on board with proper terminal ends , is worth the room it takes.
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Old 10-21-2020, 06:21 AM   #15
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Some info on AC wire sizing...also DC.

https://www.boatus.com/expert-advice...rect-wire-size
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Old 10-22-2020, 08:16 AM   #16
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I need to clarify some of the info that has been presented up thread as there is some conflation. Note: I did not watch the link provided by @psneeld #15.

When specifying a conductor to use in an electrical circuit aboard a boat where the ABYC Standards are used, there are two physical properties to consider; conductor ampacity and voltage drop. For AC circuits only ampacity need be considered whereas for DC circuits both ampacity and voltage drop need to be considered. My experience has shown that if a DC circuit is sized properly for voltage drop, then ampacity requirements will be generally met.

From a practical point of view, ampacity is the ability of a conductor to carry current without melting the insulation (or the copper, for that matter.). "Boat Cable", an actual UL designation (UL1426) is most commonly used in the USA (Ancor, Corbra, Pacer, etc.) has insulation rated at 105C dry/75C wet. Look at a piece of Boat Cable and you will see this marking every foot along the conductor. BTW, Boat Cable is not required to be tinned.

Ampacity is also affected by the ambient temperature of the conductor's environment and any bundling with other current carrying conductors.

The ABYC Standards have two environmental temperatures to consider on a boat: in a machinery space (50C) and every place else (30C). The ampacity of a Boat Cable is derated if it is used inside a machinery space. Similarly, the ampacity of a Boat Cable is derated if it is bundled. The ABYC Ampacity Tables provide for these conditions.

Voltage drop is a function of conductor composition (always copper for Boat Cable) and circuit length. For DC systems, ABYC specifies a maximum voltage drop of 3% for critical loads (bilge blowers, navigational lights, etc.) and 10% for everything else. At the lengths of vessels commonly discussed on Trawler Forum, circuit length is not a factor for AC circuits.

So, back to the OP regarding sizing the conductor: Assuming a single 1200W heating element; the maximum current would be I = P/V > 1200W/120V = 10AAC.

From ABYC E-11, Table 6C (and other sources): 16AWG Boat Cable bundled with up to 6 current carrying conductors has an ampacity of 12.8AAC in the Engine Room. Personally I would use AWG14 Boat Cable with an ampacity of 17.9AAC in the E/R.

I have no opinion on the switch. For the OP, IYB (It's Your Boat).

Hope this helps.
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Old 10-22-2020, 05:09 PM   #17
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Quote:
Originally Posted by CharlieJ View Post
I need to clarify some of the info that has been presented up thread as there is some conflation. Note: I did not watch the link provided by @psneeld #15.

When specifying a conductor to use in an electrical circuit aboard a boat where the ABYC Standards are used, there are two physical properties to consider; conductor ampacity and voltage drop. For AC circuits only ampacity need be considered whereas for DC circuits both ampacity and voltage drop need to be considered. My experience has shown that if a DC circuit is sized properly for voltage drop, then ampacity requirements will be generally met.

From a practical point of view, ampacity is the ability of a conductor to carry current without melting the insulation (or the copper, for that matter.). "Boat Cable", an actual UL designation (UL1426) is most commonly used in the USA (Ancor, Corbra, Pacer, etc.) has insulation rated at 105C dry/75C wet. Look at a piece of Boat Cable and you will see this marking every foot along the conductor. BTW, Boat Cable is not required to be tinned.

Ampacity is also affected by the ambient temperature of the conductor's environment and any bundling with other current carrying conductors.

The ABYC Standards have two environmental temperatures to consider on a boat: in a machinery space (50C) and every place else (30C). The ampacity of a Boat Cable is derated if it is used inside a machinery space. Similarly, the ampacity of a Boat Cable is derated if it is bundled. The ABYC Ampacity Tables provide for these conditions.

Voltage drop is a function of conductor composition (always copper for Boat Cable) and circuit length. For DC systems, ABYC specifies a maximum voltage drop of 3% for critical loads (bilge blowers, navigational lights, etc.) and 10% for everything else. At the lengths of vessels commonly discussed on Trawler Forum, circuit length is not a factor for AC circuits.

So, back to the OP regarding sizing the conductor: Assuming a single 1200W heating element; the maximum current would be I = P/V > 1200W/120V = 10AAC.

From ABYC E-11, Table 6C (and other sources): 16AWG Boat Cable bundled with up to 6 current carrying conductors has an ampacity of 12.8AAC in the Engine Room. Personally I would use AWG14 Boat Cable with an ampacity of 17.9AAC in the E/R.

I have no opinion on the switch. For the OP, IYB (It's Your Boat).

Hope this helps.
Sometimes it's important to explain things to the forum to clear up misconceptions. ABYC is a self regulating body comprised of boat builders who generate standards of the barest minimum for new construction (please correct me if I'm wrong). Their standards are nothing like inspected vessel codes and the wouldn't meet residential housing codes for 120 VAC wiring. They're the barest minimum.

Consider the OP's original post. Let's assume he decides to replace the wire run from breaker panel to the new water heater location and assume he needs 50' of new wire. Going to a popular online site for boat wire, I find the difference between 14/3 and 10/3 industry standard, made in the USA, tinned multi stand wire is less than $30. Considering this appliance could be on continuously for hours, why would you attempt to use the minimum and incur voltage loss (reduced performance) to save $30? Finally, should you have to replace the water heater and ended up with a higher wattage one, why would you not want the higher capacity wire in place to handle it?

Ted
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Old 10-22-2020, 05:37 PM   #18
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While boats often break some of the NEC rules for home wiring, any splice should be in a junction box. So why not use the switch?

10 gauge would be rather healthy. 14 gauge would meet code if the circuit has a 15 amp breaker. 1 volt of drop is a lot for a 12V circuit, but peanuts for a 110V AC circuit.

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The codes you need are from AYBC and/or ABS, NEC rules are NOT for marine installations.
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Old 10-22-2020, 06:02 PM   #19
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ABYC is a self regulating body comprised of boat builders who generate standards of the barest minimum for new construction (please correct me if I'm wrong). Their standards are nothing like inspected vessel codes and the wouldn't meet residential housing codes for 120 VAC wiring. They're the barest minimum.
You are wrong regarding the composition of the various committees. ABYC works hard to ensure that the committee composition includes surveyors, boatbuilders, marine equipment manufacturers, Underwriter Labs, USCG and artisans like me. No one market segment can dominate a committee. They are not just for new construction but are also to be used for refit, repair and upgrading.

In fact the source for the ampacity tables came from the NEC although the recreational marine industry specifies stranded Type 2 or Type 3 wire and the NEC tables are for solid wire. Circular mils are circular mils.

The Standards are, in fact, referenced in the CFR, and while they represent the minimum requirements for safety they are codified and becoming homogenized with the ISO standards.

As I said, the minimum, which will operate at full amperage without overheating, is 16/3. I would personally use 14/3, if for no other reason than it is more mechanically robust. 10/3 would be overkill and I would have difficulty justifying the additional cost to my client. And for AC, 10' or 50', makes no difference as voltage drop is not part of the equation.
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Old 10-22-2020, 06:15 PM   #20
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As I said, the minimum, which will operate at full amperage without overheating, is 16/3. I would personally use 14/3, if for no other reason than it is more mechanically robust. 10/3 would be overkill and I would have difficulty justifying the additional cost to my client. And for AC, 10' or 50', makes no difference as voltage drop is not part of the equation.
Considering what you charge per hour, would the additional $30 be more than 5% of your bill?

Do you usually go below the original standard of the boat builder? From the original post it appears the boat builder set his standard at 10 gauge.

It's clear that some builders standards far exceed the minimum of ABYC.

Ted
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