The boat came in on a 100A cord with a dead Charles Iso-Boost 100.
That cabinet had done the job for years: 24 kVA, isolation, automatic boost when the marina sat on 208V. Charles Marine no longer builds it. The yard needed 24 kVA back, in a space that was never generous, without waiting on a used 100A steel box from a forum listing.
They did not need another 400-plus-pound can. They needed the Iso-Boost 100 job done with hardware that could actually go back in the boat.
The order was two Dual MP6 systems. Four pucks. 24 kVA. Custom 5 ft leads so the pucks could sit where the old cabinet never could.
One Dual MP6 would have been the Iso-Boost 50 quote. That is 12 kVA. This page is the 100A boat.
What the crew was looking at
The Iso-Boost 100 is one laminated isolation-and-boost transformer in a tall metal enclosure. 24 kVA. 100A, 208/240V in. 120/240V out. Automatic ~15% boost. Soft start on that Charles SKU. A hoist ticket.
Two Dual MP6 systems are four toroidal pucks. Each puck is 12.6 in across and 6.5 in high, about 80 lb, hermetically sealed in flame-rated ABS. Soft start included. 104V and 208V taps included. Combined 320 lb, split across two lockers if the stringer bay is gone.
| Failed Iso-Boost 100 | What went back on the boat | |
|---|---|---|
| Rating | 24 kVA / 100A | 24 kVA / 100A class |
| Package | One steel boost cabinet | Four Dual MP6 pucks |
| Weight in one lift | Hundreds of pounds | 80 lb per puck |
| Height | Tall can | 6.5 in |
| Boost | Automatic ~15% | 104/208V taps |
| Soft start | Charles board | Included on each Dual MP6 |
| Leads on this job | Cabinet terminals | Custom 5 ft leads |
| Core | Laminated stack | Toroidal |
The upgrade was not a sticker. It was that the replacement fit the boat the original unit had been fighting.
How the retrofit actually went
The old cabinet owned one bay. Pulling it was the easy half. Finding a same-size 24 kVA steel replacement was the hard half. Used Iso-Boost 100 inventory is thin. Form-fit imports exist. They are still tall metal boxes.
The Dual MP6 path was different. Four low pucks. Two systems. The yard split them: a pair where the Charles can had sat, a pair in a second locker that never would have taken a 24 kVA cabinet. That is the point of 6.5 in of height.
Custom 5 ft leads were on the PO because the new landing spots were not the old terminal block. Five feet let the electrician keep the pucks out of the bilge splash and still reach the 100A panel without a mid-span splice in a wet bay. Stock leads would have forced the pucks back into the exact footprint they were trying to leave.
Landing was two Dual MP6 diagrams, not one Charles drawing. Each system got its own secondary neutral-to-ground bond per the print. Shore green capped. 100A-class conductors on the 100A inlet. Breakers sized for 24 kVA, not for one 12 kVA pair.
When they closed the pedestal, soft start on each Dual MP6 took the inrush. The 100A ELCI stayed closed. That is the first test a 24 kVA swap has to pass. A pair of “plain” 12 kVA isolation boxes with no inrush limit fails that test before the zincs ever matter.
How Dual MP6 does the Iso-Boost 100 job
Charles put isolation, boost, and soft start in one control-and-iron cabinet. Dual MP6 splits the same jobs across the winding and the taps.
| Job the 100A boat needs | How Dual MP6 does it |
|---|---|
| 24 kVA continuous | Two Dual MP6 systems (12 + 12) |
| Isolation from shore ground | Galvanic isolation, Class II pucks, green capped |
| 208V or sagging dock | 104V and 208V taps, wired on both systems |
| Pedestal does not trip on first close | Soft start on each Dual MP6 |
| Gear that survives the locker | Hermetic epoxy in flame-rated ABS |
| Fit a boat that already lost its bay | Four 6.5 in pucks, custom lead length |
Boost is the honest difference. Iso-Boost 100 watched dock voltage and switched itself. Dual MP6 does not clone that automatic board. The taps are on the unit. The electrician lands 208V boost when the marina is a 208V marina. Same dock problem. Different method. Put that sentence in the quote so nobody expects a Charles SAFEtech clone.
Boost also costs current. A plant already sitting at 100A on a 208V pedestal is not getting a free 24 kVA at 240V. Size the load on both systems.
Why the toroidal core is the upgrade
The Iso-Boost 100 was a laminated stack in a steel can. That works. It also wastes space and dumps heat into a locker that already has engines, chargers, and poor air.
A toroidal core keeps the flux in a closed ring. Leakage drops. Copper path shortens. The same 12 kVA runs in an 80 lb puck instead of half a steel cabinet. Bridgeport winds these in the high 90s for efficiency, upwards of 98% on the Dual MP6 duty. That is not a brochure adjective. It is why the locker needs less air movement after the swap.
Heat is the part owners feel. A laminated 24 kVA box in summer is a space heater next to the battery bank. Two Dual MP6 systems at high efficiency leave more of the 24 kVA in the air conditioners and less of it in the stringer bay. Less heat is also why a sealed puck can live in a tight space a vented steel can could not.
Quiet follows the same geometry. A toroid does not have the stacked-laminate buzz a 24 kVA Iso-Boost 100 puts into a quiet boat at night. Crews notice that before they notice the kVA math.
What the casing is doing in a wet locker
Each Dual MP6 winding is hermetically sealed in epoxy inside flame-rated ABS. No steel can to rust. No case used as a ground reference. Class II isolation. Ignition protected. UL Listed Marine, file E509703.
That package is why four pucks can sit lower and wetter than the Charles cabinet was designed to sit. The Iso-Boost 100 assumed a dry, structured bay and a hoist. Dual MP6 assumes a locker, a splash, and two people moving 80 lb at a time.
Custom 5 ft leads do not change that seal. They keep the sealed body in the dry-enough spot and send copper to the panel.
100A inlet or two 50A inlets
This boat was a true Iso-Boost 100: one 100A inlet, 24 kVA.
| Inlet on the boat | Order |
|---|---|
| One 100A, 125/250V | Two Dual MP6 systems, split or paralleled per the drawing |
| Two 50A, 125/250V | Two Dual MP6 systems, one per inlet |
Same four pucks. Different drawing. A reverse-Y that builds 100A from two dock receptacles still needs 24 kVA on the boat. The Y is not the transformer.
Weight that actually moved
| Old Iso-Boost 100 class | What the yard handled | |
|---|---|---|
| One lift | One steel cabinet | Never again on this boat |
| Each lift | 80 lb | |
| Total iron on board | Hundreds of pounds in one place | 320 lb in four places |
| Second locker | Unusable for the Charles can | Used |
That is the story owners repeat. Not “toroidal.” “We finally put isolation back without giving the whole bay to a box.”
Hubbell 100A is a different story
Hubbell’s HBL100AIT class is 25 kVA / 100A, about 250 lb, optional auto-boost, steel or 316 SS. If the yard wants one 25 kVA metal 100A box, that is that conversation. This retrofit wanted height, split mount, and leads. Two Dual MP6 systems. State 24 kVA vs 25 kVA. Do not blur them.
FAQ
What replaces an Iso-Boost 100?
Two Dual MP6 systems. 24 kVA. Four pucks.
Can one Dual MP6 replace an Iso-Boost 100?
No. That is 12 kVA.
Why custom 5 ft leads?
So the pucks can sit in lockers the old cabinet could not use and still reach the 100A panel without a wet splice.
Is Dual MP6 automatic boost like Charles?
No. 104/208V taps plus soft start. Same 208V dock problem. Different method.
Why is the locker cooler?
Toroidal Dual MP6 runs in the high 90s, upwards of 98% efficient. Less of the 24 kVA becomes heat.
Will four pucks bolt into the Iso-Boost 100 holes?
No. That is the point of the retrofit.
Where is Dual MP6 made?
Shelton, Connecticut.
Product Callout
Bridgeport Magnetics MarinePuck Dual MP6
Iso-Boost 100 replacement is two Dual MP6 systems (24 kVA / 100A class). Custom lead lengths available. Soft start and 104/208V boost included. Hermetically sealed flame-rated ABS. UL Listed Marine, ignition protected, made in the USA.
Phone: (203) 954-0050
Email: [email protected]
bridgeportmagnetics.com/product/marine-puck-dual-mp6-50a
