Empathy List Archives

JH

Jim Healy

Mon, Jul 28, 2008 12:30 PM

Steve Willett Wrote:

SNIP>
The question which stared it all was which would be best for a boat with
two- 30 amp inputs when a 50 amp outlet is available on the dock, a splitter
dock side and two 30 amp cables to the boat or to run a 50
amp cable to the boat and the Y splitter at the inputs.

The discussion is that two 30 amp cables are cheaper and easier to handle
than a 50 amp cable. The other side says it is dangerous to use that set up
because of the breaker sizing on the 50 amp outlet being to high to protect
in case of an overload on one of the 30 amp cables and creating a possible
fire hazzard.
ENDSNIP>

Steve,

The shore power supply choice is not be based on the breaker discussion. IT
IS ALWAYS OK TO USE WIRING WITH LARGER AMPACITY RATINGS THAN THE ESTIMATED
OVERLOAD MARGIN. THE LARGER, THE BETTER. In the real world, this is
limited by cost, convenience, etc, but never by the physics of Ohm's Law.

The purpose of fuses/breakers is to protect the WIRING ATTACHED TO THAT
BREAKER, not (as most people believe) attached devices. The 50A breaker
on the dock pedestal is to protect (shore power) wiring attached to that
breaker. That design point is fine if you're attaching a boat fitted with
50 Amp wiring and connectors. (Dock wiring to the pedestal itself is
protected at a utility cabinet closer to the Service Entrance.) An overload
in one leg of a 230V, 50A circuit should trip both legs due the the
mechanical link that attaches the two breaker halves together on a 230V
breaker. And yes, that overload would generally be in excess of 50 Amps.

In the case of a boat fitted with 30A wiring, the 2-pole 30A disconnect
breaker located on the boat and within 72 inches of the 30A shore power
inlet connector will also protect the shore power cord from OVERLOAD, since
it's a DEDICATED POINT-TO-POINT ATTACHMENT. So, if you're drawing in excess
of 30A but less than 50A, that onboard disconnect will protect the shore
power cord (and the boat wiring up to the 2-pole 30A disconnect breaker
located on the boat and within 72 inches of the 30A shore power inlet
connector).

The real issue is this: loose/corroded connections on the shore power
cord-ends, the terminal blades, or at the inlet housing, or all of those
points together, can indeed cause a fire in the onboard electrical locker,
but the 2-pole 30A disconnect breaker located on the boat within 72 inches
of the 30A inlet connector might well not trip, because there might well not
be a true "overload;" just high resistance that generates enuf heat to get
plastic to smolder, then erupt into flame. Don't ask how I know.

Peg and Jim Healy aboard Sanctuary,
currently at Rock Creek, Pasadena, MD

Steve Willett Wrote: SNIP> The question which stared it all was which would be best for a boat with two- 30 amp inputs when a 50 amp outlet is available on the dock, a splitter dock side and two 30 amp cables to the boat or to run a 50 amp cable to the boat and the Y splitter at the inputs. The discussion is that two 30 amp cables are cheaper and easier to handle than a 50 amp cable. The other side says it is dangerous to use that set up because of the breaker sizing on the 50 amp outlet being to high to protect in case of an overload on one of the 30 amp cables and creating a possible fire hazzard. ENDSNIP> Steve, The shore power supply choice is not be based on the breaker discussion. IT IS ALWAYS OK TO USE WIRING WITH LARGER AMPACITY RATINGS THAN THE ESTIMATED OVERLOAD MARGIN. THE LARGER, THE BETTER. In the real world, this is limited by cost, convenience, etc, but never by the physics of Ohm's Law. The purpose of fuses/breakers is to protect the WIRING ATTACHED TO THAT BREAKER, *not* (as most people believe) attached devices. The 50A breaker on the dock pedestal is to protect (shore power) wiring attached to that breaker. That design point is fine if you're attaching a boat fitted with 50 Amp wiring and connectors. (Dock wiring to the pedestal itself is protected at a utility cabinet closer to the Service Entrance.) An overload in one leg of a 230V, 50A circuit should trip both legs due the the mechanical link that attaches the two breaker halves together on a 230V breaker. And yes, that overload would generally be in excess of 50 Amps. In the case of a boat fitted with 30A wiring, the 2-pole 30A disconnect breaker located on the boat and within 72 inches of the 30A shore power inlet connector will also protect the shore power cord from OVERLOAD, since it's a DEDICATED POINT-TO-POINT ATTACHMENT. So, if you're drawing in excess of 30A but less than 50A, that onboard disconnect will protect the shore power cord (and the boat wiring up to the 2-pole 30A disconnect breaker located on the boat and within 72 inches of the 30A shore power inlet connector). The real issue is this: loose/corroded connections on the shore power cord-ends, the terminal blades, or at the inlet housing, or all of those points together, can indeed cause a fire in the onboard electrical locker, but the 2-pole 30A disconnect breaker located on the boat within 72 inches of the 30A inlet connector might well not trip, because there might well not be a true "overload;" just high resistance that generates enuf heat to get plastic to smolder, then erupt into flame. Don't ask how I know. Peg and Jim Healy aboard Sanctuary, currently at Rock Creek, Pasadena, MD

J

joe

Mon, Jul 28, 2008 1:46 PM

Hello All, When my boat was being built I naively wanted twin power inlets
of 120v/30 amp and 240v/50 amp. Several boat owners advise me that it was
not necessary. They said with the single 240v/50 amp inlet and adapters all
combinations of available power from 240v/50amp, 120v/30amp, to 120v/20amp
can be tapped, albeit with necessary careful power management. I have used
all these combinations in the course of my cruising, even plugging into a
single 120/15amp household type plug. Understand that very very strict
power demand management must be used. When on the 120v/15/20amp plug I
would only run the frig. and a light or two and have the batteries at max
charge so the charger was on trickle or turn it off. Of course this assumes
that the boat is wired to take advantage of this option by powering the
correct 120 leg.
In my case the leg with the inverter/charger. I also go the great length to
protect the adapter connections with corrosion block and a wrap of fusion
tape for weather resistance. I've been cautioned that there is smoke in the
wires that must not be let out!

Currently at anchor behind the Statue of Liberty preparing to cruise up the
East River into Long Island Sound.

Joe
"Carolyn Ann"

-----Original Message-----
From: trawlers-and-trawlering-bounces@lists.samurai.com
[mailto:trawlers-and-trawlering-bounces@lists.samurai.com] On Behalf Of Jim
Healy
Sent: Monday, July 28, 2008 8:30 AM
To: trawlers-and-trawlering@lists.samurai.com
Subject: T&T: Power Cord

Steve Willett Wrote:

SNIP>
The question which stared it all was which would be best for a boat with
two- 30 amp inputs when a 50 amp outlet is available on the dock, a splitter
dock side and two 30 amp cables to the boat or to run a 50
amp cable to the boat and the Y splitter at the inputs.

The discussion is that two 30 amp cables are cheaper and easier to handle
than a 50 amp cable. The other side says it is dangerous to use that set up
because of the breaker sizing on the 50 amp outlet being to high to protect
in case of an overload on one of the 30 amp cables and creating a possible
fire hazzard.
ENDSNIP>

Hello All, When my boat was being built I naively wanted twin power inlets of 120v/30 amp and 240v/50 amp. Several boat owners advise me that it was not necessary. They said with the single 240v/50 amp inlet and adapters all combinations of available power from 240v/50amp, 120v/30amp, to 120v/20amp can be tapped, albeit with necessary careful power management. I have used all these combinations in the course of my cruising, even plugging into a single 120/15amp household type plug. Understand that very very strict power demand management must be used. When on the 120v/15/20amp plug I would only run the frig. and a light or two and have the batteries at max charge so the charger was on trickle or turn it off. Of course this assumes that the boat is wired to take advantage of this option by powering the correct 120 leg. In my case the leg with the inverter/charger. I also go the great length to protect the adapter connections with corrosion block and a wrap of fusion tape for weather resistance. I've been cautioned that there is smoke in the wires that must not be let out! Currently at anchor behind the Statue of Liberty preparing to cruise up the East River into Long Island Sound. Joe "Carolyn Ann" -----Original Message----- From: trawlers-and-trawlering-bounces@lists.samurai.com [mailto:trawlers-and-trawlering-bounces@lists.samurai.com] On Behalf Of Jim Healy Sent: Monday, July 28, 2008 8:30 AM To: trawlers-and-trawlering@lists.samurai.com Subject: T&T: Power Cord Steve Willett Wrote: SNIP> The question which stared it all was which would be best for a boat with two- 30 amp inputs when a 50 amp outlet is available on the dock, a splitter dock side and two 30 amp cables to the boat or to run a 50 amp cable to the boat and the Y splitter at the inputs. The discussion is that two 30 amp cables are cheaper and easier to handle than a 50 amp cable. The other side says it is dangerous to use that set up because of the breaker sizing on the 50 amp outlet being to high to protect in case of an overload on one of the 30 amp cables and creating a possible fire hazzard. ENDSNIP>

RR

Ron Rogers

Mon, Jul 28, 2008 2:19 PM

In addition to the wise advice below, you must have a balanced load between
the two 30amp cables if your design has them both attached at the same time
and feeding either side of an AC panel. The previous owner's yard did not do
this and I ended-up with a very small fire on my port inlet. That inlet fed
direct to a contiguous double-pole breaker.

To balance the load, you have to think through what is normally turned on in
the Summer. For example, if you have two A/C units on board, place their
breakers on opposite sides of your AC panel. Try to offset the hot water
heater with something that draws similar amperage like a conventional
refrigerator.

Lastly, buy Hubbell AC cables and components instead of Marinco. Hubbell
cable ends are swaged to the wires, not screw-clamped. Consumer's Marine had
the best pricing on Hubbell *last time I checked." Regardless of
manufacturer, use CRC silicone grease on all inlets, outlets, and cable
ends. This has prevented scorching and oxidation (reduces conductivity and
increases amperage) on my boat. Also, I've used a Hubbell 50A cable from
shore to boat and then placed a splitter to attach the cable to my 30A
inlet. I used the other leg of the splitter to attach an extension cord for
when I am working on the boat - powering a vacuum cleaner and powertool, for
example.

Ron Rogers

----- Original Message -----
From: "Jim Healy" gilwellbear@gmail.com
|
| The real issue is this: loose/corroded connections on the shore power
| cord-ends, the terminal blades, or at the inlet housing, or all of those
| points together, can indeed cause a fire in the onboard electrical locker,
| but the 2-pole 30A disconnect breaker located on the boat within 72 inches
| of the 30A inlet connector might well not trip, because there might well
not
| be a true "overload;" just high resistance that generates enuf heat to get
| plastic to smolder, then erupt into flame. Don't ask how I know.
|
| Peg and Jim Healy aboard Sanctuary,
| currently at Rock Creek, Pasadena, MD
| _______________________________________________
| http://lists.samurai.com/mailman/listinfo/trawlers-and-trawlering
|
| To unsubscribe or modify your subscription options (get password, change
email address, etc) go to:
http://lists.samurai.com/mailman/options/trawlers-and-trawlering
|
| Trawlers & Trawlering and T&T are trademarks of Water World
| Productions. Unauthorized use is prohibited.

In addition to the wise advice below, you must have a balanced load between the two 30amp cables if your design has them both attached at the same time and feeding either side of an AC panel. The previous owner's yard did not do this and I ended-up with a very small fire on my port inlet. That inlet fed direct to a contiguous double-pole breaker. To balance the load, you have to think through what is normally turned on in the Summer. For example, if you have two A/C units on board, place their breakers on opposite sides of your AC panel. Try to offset the hot water heater with something that draws similar amperage like a conventional refrigerator. Lastly, buy Hubbell AC cables and components instead of Marinco. Hubbell cable ends are swaged to the wires, not screw-clamped. Consumer's Marine had the best pricing on Hubbell *last time I checked." Regardless of manufacturer, use CRC silicone grease on all inlets, outlets, and cable ends. This has prevented scorching and oxidation (reduces conductivity and increases amperage) on my boat. Also, I've used a Hubbell 50A cable from shore to boat and then placed a splitter to attach the cable to my 30A inlet. I used the other leg of the splitter to attach an extension cord for when I am working on the boat - powering a vacuum cleaner and powertool, for example. Ron Rogers ----- Original Message ----- From: "Jim Healy" <gilwellbear@gmail.com> | | The real issue is this: loose/corroded connections on the shore power | cord-ends, the terminal blades, or at the inlet housing, or all of those | points together, can indeed cause a fire in the onboard electrical locker, | but the 2-pole 30A disconnect breaker located on the boat within 72 inches | of the 30A inlet connector might well not trip, because there might well not | be a true "overload;" just high resistance that generates enuf heat to get | plastic to smolder, then erupt into flame. Don't ask how I know. | | Peg and Jim Healy aboard Sanctuary, | currently at Rock Creek, Pasadena, MD | _______________________________________________ | http://lists.samurai.com/mailman/listinfo/trawlers-and-trawlering | | To unsubscribe or modify your subscription options (get password, change email address, etc) go to: http://lists.samurai.com/mailman/options/trawlers-and-trawlering | | Trawlers & Trawlering and T&T are trademarks of Water World | Productions. Unauthorized use is prohibited.

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Power Cord