Stack Socket Replacement

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A couple of days after we arrived into Newport, we found the breaker for the pilothouse 120V outlets had tripped. We investigated all the electronics plugged into the PH outlets but the breaker would still trip. We eventually unplugged everything and it still tripped so it had to be a bad breaker or a circuit problem. We got out the boat wiring diagram to investigate more deeply and noticed there were two more outlets on the circuit up on the boat deck. Stepping outside, the source of our issue was pretty obvious: a socket mounted on the side of the stack was showing some blackening.

Over the next few days, we sourced parts, replaced the socket box and also resealed the engine exhaust cooling vent directly above it. Details of the job from April 1st through April 5th, 2017 follow.

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The damaged socket is the same we’d founds a loose wire at when investigating a water leak in the stack while in Plymouth, NH. Two problems is too many, so we will replace the socket entirely with a water proof variant and replace the wiring that runs to the socket to ensure that all is new and dry. The parts are ordered from Amazon Prime and, for now, we have an extension cord bringing power up to the PH.
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Burned Socket
Our Amazon Prime order with replacement parts for the burned socket arrived this morning, so we started in on the repair. The damage was more extensive than we’d realized. It looks like the worst possible failure mode where some current still flowed between poles in the socket but not enough to trip the 15A breaker in the pilot house. 15A is a lot of power and can produce dangerous heating. It appears that it was leaking power between the poles for quite some time prior to the breaker eventually opening. The lower quarter of the GFCI burned away and two inches of the feed wires were burned.

We don’t know if the GFCI failed to open, but the socket still leaked current between the poles perhaps due to water intrusion. It’s a good thing that the breaker protected the circuit correctly. If that breaker had failed to open, then there is a 30A breaker “north” of the 15A but that would require twice the fault current to release.

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Work in Progress
We removed the old burned-up unit, cleaned up the 5200 that sealed the square stack opening and any loose core material, and sealed up the stack core with epoxy. Here James is smoothing down a marine-board plate that we’ll use to cover the hole and mount the new box.
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The plate in place, covering the hole where the old socket mounted into the stack.
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New Box
Sealing the new outdoor-safe power box to the plate with silicone. It’s a 100% sealed-up aluminum box with only two openings. The one in front will be sealed by an outdoor-certified socket cover and one in the back will be sealed by an outdoor-safe power wire gland.
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Burned Wire
This is the original feed wire that connected to the back of the socket. Two inches were burned.
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Wiring Socket
James pulling a new feed wire to replace the damaged one.
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Connecting Power
Connecting the other end of the feed wire to the junction box. There are no easy-to-get-at places in the stack, but this one was particularly difficult.
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Completed Job
This finished job looks pretty good and definitely is weather-safe.
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The burned socket was well-sealed against the elements both inside and outside the stack, so it wasn’t clear what caused the water-induced current leakage. Closer inspection of the engine exhaust cooling vent directly above the socket revealed that the vent is sealed on the outside but there is exposed foam core on the inside. The water is flowing down the inside of the stack when it’s really wet, entering the foam core of the stack at the exhaust cooling vent, and flowing down to the socket. Since the socket was well sealed against water entering (or exiting), it just filled up with water.

It’s bad news to have water entering foam cores, we had another job ahead of us to remove the exhaust vent, cut back the foam, and epoxy fill the void to seal off the core and then replace the fitting.

We started that job this morning and on removing the vent we saw that the foam core temperature had been high enough over the years to darken it. This vent is the exit for the exhaust stack cooling system. Air leaves this vent surprisingly hot—we’ve seen temperatures as high as 250°F. There’s an air gap between the pipe and the surrounding fiberglass, and the only point of contact is the flange. We chose to mitigate the temperature issue in three parts: 1) cut back the foam core a half-inch beyond the edge of the fiberglass and seal it with epoxy, leaving an even large air gap to the foam, 2) put two layers of fibrous high-temperature exhaust gasket between the flange and the fiberglass, and 3) put an insulating layer of the same material around the pipe where it exits through the side of the stack, while still leaving an air gap.

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We cleaned up the core and sealed it with five-minute epoxy.
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Preparing to cut the insulating fibrous high-temperature exhaust gasket.
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Two gasket collars installed on the exhaust vent.
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Ready to Re-install
The now-insulated stack vent ready to re-install. The fibrous insulation material is exhaust gasket, rated well beyond 1,000°F. The strip of tape used to hold the insulation at the hole through the stack is rated at 450°F, so has lots of engineering headroom for this cooling air application. The tape is only needed to hold the insulation in place around the pipe during installation.

An additional potential gain from this work is we used to have a small water leak, just a small drip, into the engine room during very heavy rains. It appears that water may have been coming in through the foam core at the exhaust cooling vent. We’ve had one very large rain since then with no evidence of leakage.


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8 comments on “Stack Socket Replacement
  1. Steve Coleman says:

    With today’s commercial HVAC equipment, the ECM’s tend to do everything they can to save the equipment.

    I know we’ve been able to pin down what normally would seem at first glance to be a nuisance trip to failing disconnects and breakers using a infra red camera.

    I don’t know if that would be something you’d find a use for on Dirona especially one like I carry however, if you get one run off a Android or I Phone they tend to be fairly cheap.

  2. Jamie W says:

    Seems like a bit of a design flaw not to have the outside outlets on a separate (lower-rated) breaker? Or a separate switch in the pilothouse, for that matter.

    • Jamie, I had this socket added while the boat was commissioned — it’s not part of the standard Nordhavn install. Generally for outside sockets or inside, they typically are on 15A circuits in North America so nothing unusual there.

      The new junction box is a much better design unlikely to let water in. As an extra level of protection we have put arc fault and ground fault circuit interrupters on all circuits on Dirona whether they are inside or outside. All circuits are not protected. So, looking at this socket, we have it sealed, it is a AFCI/GFCI socket, then we have a 15A breaker and then “above” that we have a 33A breaker. Overall I like the new design.

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