A Charles 50A isolation transformer is the 12 kVA unit yards have installed for years. The common SKUs are the Charles IsoTransformer 93-IXFMR12I-A / 93-IXFMR12T-A and the Charles Iso-Boost 50. Both are 12 kVA, 50A, 120/240V class machines.
Some boats show up with two Charles Iso-Boost 50s. That is not a 12 kVA job. Two 12 kVA units are 24 kVA. Charles also sells that class as a single Iso-Boost 100.
The Bridgeport Magnetics equivalent is the MarinePuck Dual MP6 50A at 12 kVA, or two Dual MP6 systems at 24 kVA.
It is not a bolt-for-bolt copy of the Charles box. Charles 12 kVA is one 235 lb metal enclosure. Dual MP6 is two 80 lb pucks (160 lb total).
Drop-in replacement at a glance
| You have | kVA / shore | What to order |
|---|---|---|
| Charles IsoTransformer 12 kVA (93-IXFMR12I-A or 12T-A) | 12 kVA, one 50A 240V cord | One Dual MP6 50A |
| Charles Iso-Boost 50 | 12 kVA, one 50A cord | One Dual MP6 50A |
| Two Charles Iso-Boost 50s | 24 kVA, two 50A cords | Two Dual MP6 50A systems (four pucks) |
| Charles Iso-Boost 100 | 24 kVA, 100A class | Two Dual MP6 50A systems (four pucks) |
| Charles 3.6 kVA (30A) | 3.6 kVA, 30A 120V | MP3.6, not Dual MP6 |
Electrical drop-in at 12 kVA: yes.
Mechanical drop-in: no. Plan pucks, not the Charles bolt pattern.
12 kVA vs 24 kVA, before you ask for quote
| Setup | Continuous kVA | Typical shore | Charles weight class | MarinePuck |
|---|---|---|---|---|
| One IsoTransformer or one Iso-Boost 50 | 12 kVA | One 50A / 240V | 235 lb | One Dual MP6, 160 lb |
| Two Iso-Boost 50s | 24 kVA | Two 50A cords | About 470 lb | Two Dual MP6, 320 lb |
| One Iso-Boost 100 | 24 kVA | 100A class | About 550 lb and up | Two Dual MP6, 320 lb |
50A × 240V = 12 kVA. That is one Dual MP6.
Two of those shore cords, or an Iso-Boost 100, is 24 kVA. That is two Dual MP6 kits (four 80 lb pucks).
Charles 12 kVA vs Dual MP6
| Spec | Charles IsoTransformer 12 kVA | Charles Iso-Boost 50 | MarinePuck Dual MP6 50A |
|---|---|---|---|
| Continuous rating | 12 kVA | 12 kVA | 12 kVA |
| Shore service | 50A, 240V | 50A, 208/240V | Dual 50A, 120/240V |
| Input / output | 120/240V (I-A also 104/208 taps) | 120/240V, auto boost | 120/240V, 104V and 208V boost included |
| Frequency | 50/60 Hz | 50/60 Hz | 50/60 Hz |
| Published weight | 235 lb | 235 lb | 160 lb (two 80 lb units) |
| Package | One metal box, about 16 × 15 × 12 in | One metal box, 18 × 15 × 12 in | Two pucks, 12.6 in OD × 6.5 in H each |
| Core | Laminated | Laminated | Toroidal |
| Enclosure | Corrosion-resistant metal | Metal | Flame-rated ABS, epoxy potted |
| Soft start | Not standard on basic IsoTransformer | Included on Iso-Boost | Included |
| Boost | Taps on I-A, or buy Iso-Boost / SmartBoost | Automatic boost, 42.5A max in boost | 104V and 208V included |
| Case grounding | Metal case, ABYC-style shield | Metal case | Class II, green capped |
| Marine listing | Marine UL on many Charles models | Marine UL | UL Listed Marine E509703, ignition protected |
| Origin | Charles Marine line | Charles Marine line | Made in Shelton, Connecticut |
What “drop-in” means on the boat
A 12 kVA replacement is drop-in when:
- Shore is still one 50A, 240V cord
- The new unit is still 12 kVA continuous
- Isolation still breaks the shore-ground galvanic path
- The panel still sees 120/240V
A 12 kVA replacement is not drop-in when you expect Dual MP6 to use the same four bolt holes as a Charles 93-IXFMR12. You gain the right to split the iron: one puck to port, one to starboard, or both under a settee.
A 24 kVA replacement is drop-in only when you order two Dual MP6 systems. One Dual MP6 on a boat that already ran two Iso-Boost 50s will be asked to carry twice its rating.
Charles Iso-Boost 50 automatic 208/240 switching is not the same circuit as Dual MP6 104/208 taps. Same dock-voltage problem. Different method.
Why yards replace Charles 50A iron
Weight on a 12 kVA swap. 235 lb vs 160 lb. Each Dual MP6 puck is 80 lb. Two people can stage it without a hoist. Charles 12 kVA manuals call out hoisting holes and a structure that can hold about 250 lb.
Weight on a 24 kVA swap. Two Iso-Boost 50s are about 470 lb. One Iso-Boost 100 is in the 550 lb class. Two Dual MP6 systems are 320 lb in four 80 lb lifts.
Soft start. A dead 12 kVA transformer inrush will trip a marina ELCI or a weak pedestal. Dual MP6 includes a slow-start thermistor on every unit. Basic Charles IsoTransformer does not. Iso-Boost adds soft start on the premium SKU.
Boost without a second part number. Charles 93-IXFMR12I-A has 104/208 taps. Iso-Boost 50 is the automatic package. Dual MP6 ships with 104V and 208V boost included.
Corrosion and ignition space. Dual MP6 is a sealed non-metallic puck, Class II, ignition protected. There is no steel can to rust in a bilge.
Noise. Toroidal cores do not hum like a laminated stack on a quiet boat.
What Charles still does in one box
If the yard wants a single familiar steel enclosure and a Charles footprint that already exists in the stringers, the 12 kVA IsoTransformer stays the easy mechanical choice. If the boat needs automatic 208-to-240 switching under way, Iso-Boost 50 is built for that control scheme.
Dual MP6 wins when the constraint is weight, split mounting, included soft start and boost, or a non-metallic ignition-protected package. Two Dual MP6 systems win the same argument at 24 kVA.
Sizing check before you order
| Shore cord | Charles unit people name | MarinePuck |
|---|---|---|
| 30A, 120V | Charles 3.6 kVA IsoTransformer | MP3.6 |
| 50A, 120V | Charles 6 kVA class | Single MP6 |
| 50A, 240V | Charles 12 kVA IsoTransformer or Iso-Boost 50 | One Dual MP6 50A |
| Two 50A / 240V cords | Two Iso-Boost 50s | Two Dual MP6 50A systems |
| 100A class | Charles Iso-Boost 100 / 24 kVA | Two Dual MP6 50A systems |
Do not use a single MP6 (6 kVA) as a Charles 50A / 240V replacement.
Do not use one Dual MP6 as a two-Iso-Boost-50 replacement.
ABYC and listing, stated cleanly
Charles publishes Marine UL on many isolation and Iso-Boost models and ABYC-style shielding on the metal can.
MarinePuck Dual MP6 is UL 1561 Recognized, UL Listed Marine (E509703), and ignition protected. It is designed for ABYC E-11 isolation-transformer practice when installed to the supplied diagrams, including the secondary neutral-to-ground bond. The green shore ground is capped. That is Class II isolation, not a metal-case shield scheme. Have a marine electrician land it.
FAQ
What is the Charles equivalent of a Dual MP6?
One Charles 12 kVA IsoTransformer (93-IXFMR12I-A / 12T-A) or one Charles Iso-Boost 50.
What replaces two Charles Iso-Boost 50s?
Two Dual MP6 50A systems. That pair is 24 kVA. One Dual MP6 is only 12 kVA.
What replaces a Charles Iso-Boost 100?
Two Dual MP6 50A systems (four pucks, 24 kVA).
Is Dual MP6 a bolt-in for a Charles 93-IXFMR12?
No. Same 12 kVA isolation job. Different footprint: two 80 lb pucks vs one 235 lb box.
Does Dual MP6 replace Iso-Boost 50 automatic boost?
For isolation plus low dock voltage, yes on capability. Automatic 208/240 control is not the same as Dual MP6 taps.
Why is Dual MP6 lighter?
Toroidal cores in epoxy-potted ABS. Charles 12 kVA uses a laminated stack in a metal enclosure.
Will Dual MP6 stop marina GFI / ELCI trips?
Isolation removes the boat from the shore-ground leakage loop. Soft start reduces inrush trips. Pedestal and cord condition still matter.
Product Callout
Bridgeport Magnetics MarinePuck Dual MP6 50A
Charles 50A isolation transformer replacement at 12 kVA. Two Dual MP6 systems replace two Iso-Boost 50s or an Iso-Boost 100 (24 kVA). Soft start and 104/208V boost included. UL Listed Marine, ignition protected, made in Shelton, Connecticut.
Phone: (203) 954-0050
Email: [email protected]
bridgeportmagnetics.com/product/marine-puck-dual-mp6-50a
