Dual 120/240 shore power, Part 2

[skipmac]

Morning update:

Unless it is very well hidden there is only one isolation transformer and it is a single 240V, 50amp unit. Verified that SP1 only is running to the transformer.

SP2 I'm guessing goes more or less directly to the electric panel. The only way to verify without the rest of my tools at home, is to disassemble the conduits and trace the wires or rig a 15' extension lead to the meter to check continuity end to end.

If SP2 does go to the panel and there is no connection to the White ground wire then this could account for the low voltage on the panel from SP2 as it would be completing the circuit through the green safety ground.

Will try to investigate further after lunch.

[Statistical]

Your got a Hardy Boys mystery there skipmac. I am wondering if the SP2 was added after later and is a hack job.

If it is supplying 120V circuits without a neutral that is serious no-no. It would be allowable if it is supplying ONLY 240V circuits off a dedicated 240V panel which doesn't connect in any way to the rest of the 120V/240V circuits coming off the isolation transformer vis SP1. However from what you describe that doesn't seem to be the case.

[s/v Jedi]

Originally Posted by skipmac

Morning update:

Unless it is very well hidden there is only one isolation transformer and it is a single 240V, 50amp unit. Verified that SP1 only is running to the transformer.

SP2 I'm guessing goes more or less directly to the electric panel. The only way to verify without the rest of my tools at home, is to disassemble the conduits and trace the wires or rig a 15' extension lead to the meter to check continuity end to end.

If SP2 does go to the panel and there is no connection to the White ground wire then this could account for the low voltage on the panel from SP2 as it would be completing the circuit through the green safety ground.

Will try to investigate further after lunch.

The normal way of dealing with that is an auto transformer. In this case, if sp2 is paralleled with the output of the isolation transformer, you may see a neutral from it’s output windings, which would act kind of like an auto transformer but not designed for it so weird voltages to be expected.

Here is the normal way: 240V without neutral out of isolation transformer as well as genset and into the inverter charger which is a 240V 60Hz model (like Victron EU models can be programmed for that). Then, on the output of the inverter/charger you get 240 from either sp, genset or inverting and feed that into an auto transformer which creates a new neutral and fixes any imbalance between both 120V legs.

[skipmac]

Originally Posted by Statistical

Your got a Hardy Boys mystery there skipmac. I am wondering if the SP2 was added after later and is a hack job.

If it is supplying 120V circuits without a neutral that is serious no-no. It would be allowable if it is supplying ONLY 240V circuits off a dedicated 240V panel which doesn't connect in any way to the rest of the 120V/240V circuits coming off the isolation transformer vis SP1. However from what you describe that doesn't seem to be the case.

Yes I have a few clues and need to investigate further but this still a bit of a mystery.

One thought, this is on a Viking sport fisherman and Viking does things right and first class so either there's something more going on that I haven't yet figured out (looking at Jedi's comments next) or this was an uninstalled option that the PO finished up incorrectly.

[skipmac]

Originally Posted by s/v Jedi

The normal way of dealing with that is an auto transformer. In this case, if sp2 is paralleled with the output of the isolation transformer, you may see a neutral from it’s output windings, which would act kind of like an auto transformer but not designed for it so weird voltages to be expected.

By SP2 paralleled with output of the iso transformer do you mean the L1 and L2 hot legs of SP2 connected directly to the L1 and L2 outputs from the transformer? If yes this doesn't seem to be the case as they are switched independently and read different voltages on the panel meter.

Maybe a little more info to clarify. On the main panel, the AC control section has two sets of three switches each. Only one switch in each set can be On at a time.

Switch Set 1
SP1 - Gen 1 - Group 1 Power

Switch Set 2
SP2 - Gen 2 - Group 2 Power

Obviously SP1 or Gen 1 select the source of power.
G1P and G2P are AC loads divided into two independent banks of breakers.
On/Off setting of G1P and G2P select which power source is supplied to each group of loads as follows:

SP1 - ON
G1 - OFF
G1P - OFF

SP1 - OFF
G1 - OFF
G2P - ON

All AC loads in Group 1 and 2 are powered by SP1. Switch off SP1 and switch on Gen1 then all loads powered by Gen1.

SP1 - On
GEN1 - OFF
G1P - OFF

SP2 - ON
GEN2 - OFF
G2P - OFF

G1P loads powered by SP1, G2P loads powered by SP2. So the power groups are powered by the source in their group when switched off or powered by the other source if the Group switch is On.

Same logic follows the rest of the switch settings.

Originally Posted by s/v Jedi

Here is the normal way: 240V without neutral out of isolation transformer as well as genset and into the inverter charger which is a 240V 60Hz model (like Victron EU models can be programmed for that). Then, on the output of the inverter/charger you get 240 from either sp, genset or inverting and feed that into an auto transformer which creates a new neutral and fixes any imbalance between both 120V legs.

This setup seems initially to be similar. There are only three wires in and out of the isolation transformer, W BLK GRN and clearly connected to SP1 cable from the dock and to SP1 switches on the panel.

SP2 has three wires only from the socket in the AC inlet box in the cockpit. W BLK GRN connected W and BLK to the hot legs from the shore power cord and the GRN to the metal shield around the socket. Since this all disappears onto conduits and through bulkheads I haven't yet traced it all but I'm about 90% certain that SP2 goes as is directly to the main electric panel.

Here is the point where I'm not clear on your information and have several questions.

- Is it possible that in this setup SP2 is somehow using a common Neutral with SP1 coming out of the isolation transformer? How or where to test this?

- Other than low voltage on SP2 if there is some kind of virtual common Neutral is there a risk in using this as is?

- Best long term solution? Add another 240V, 50 amp isolation transformer? Boat has no inverters since everything runs on AC power so there is always a generator or shore power hooked up.

[Thumbs Up]

SP2's neutral would need to come from the shore power inlet. If everything is already separated into two load groups the two 50 amp supplies would never need to be combined. You could only combine them when running from a single power source. A second 50 amp transformer would be nice to have. You could run one power source with a transformer and one without (by adding the neutral and ground wires) but would negate the safety and corrosion aspect of having one.

[ranger58sb]

Originally Posted by skipmac

Yes I have a few clues and need to investigate further but this still a bit of a mystery.

One thought, this is on a Viking sport fisherman and Viking does things right and first class so either there's something more going on that I haven't yet figured out (looking at Jedi's comments next) or this was an uninstalled option that the PO finished up incorrectly.

Ask Viking?

-Chris

[skipmac]

Originally Posted by ranger42c

Ask Viking?

-Chris

We do have a call in to Viking but haven't been able to get a call back due to the intermittent connections

[skipmac]

Well the final mystery is solved. After crawling around in the far reaches of the engine room, on the other side of the boat from all the shore power connections and the isolation transformer, ten feet forward, behind the engine and half under an air conditioner we found a second Charles isolation transformer.

So both shore power systems are properly wired through transformers which is what I expected unless the PO had jury rigged something.