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Manufacturer Resources
Product Specs
- Amperage Rating:
- 400A
- Bus Material:
- Aluminum
- Enclosure:
- NEMA 3R
- Feed Type:
- Overhead
- Fuse Clip Type:
- Class T
- Interrupt Rating:
- 100 kAIC
- Line:
- (1) #750 kcmil
- Notes:
- If Class H fuse clips are needed use catalog number WCG3HK400 (order (1) per phase). If Class R fuse clips are needed order catalog number DS56FK in addition to WCG3HK400. In order to go from T to R the device must first be converted to H.
- Number Of Wires:
- Four-wire
- Phase:
- Three-phase
- Used With:
- Barrier kits available 400A-800A fusible switches: Bottom feed-3MFSBBK, Top feed-3MFSTB
- Voltage Rating:
- 120/208V
- Wire Size:
- (2) #1/0 AWG-300 kcmil
- Department:
- Electrical
- Product Length:
- 22.54 IN
- Product Height:
- 47.5 IN
- Product Weight:
- 100 LB
- Product Width:
- 16.64 IN
B-LINE 3MFS400RT – Frequently Asked Questions
1) Can the Eaton 3MFS400RT fusible switch be installed outdoors?
Yes. The 3MFS400RT comes in a NEMA 3R enclosure, which is rain and sleet resistant, so it is suitable for outdoor wall or pad locations. It is configured for overhead feed, meaning the service conductors enter from above, so plan the mast or weatherhead accordingly.
2) What fuses does the 3MFS400RT take, and can I use Class R or Class H instead?
As shipped, the 400A switch has Class T fuse clips. To run Class H fuses, order WCG3HK400, one per phase. For Class R, order DS56FK in addition to WCG3HK400, because the device has to be converted from T to H before it can go to R. There is no direct T to R conversion.
3) Will the 3MFS400RT work on a 480V system?
No. This switch is rated 120/208V, three-phase four-wire. For a 277/480V service you need a switch rated for that voltage; installing a 208V-rated device on 480V is not acceptable.
4) What size conductors will land in the Eaton 3MFS400RT main switch?
The line side takes (1) #750 kcmil per phase. Load side wire size is (2) #1/0 AWG through 300 kcmil, so you can parallel two conductors per pole. Bus is aluminum, so use a compatible AL/CU rated lug and the correct compound where required.
5) Is the 3MFS400RT rated for a high fault-current service?
It carries a 100 kAIC interrupting rating, which covers most utility services where available fault current at the service point is high. Confirm your utility's available fault current is at or below that figure.
6) Do I need a barrier kit with this 400A fusible switch?
Barrier kits are offered for 400A through 800A fusible switches: 3MFSBBK for bottom feed and 3MFSTB for top feed. They are separate catalog numbers, not included, so add the one matching your feed arrangement.
7) How big is the 3MFS400RT and can one person set it?
It measures 47.5 in high, 22.54 in long and 16.64 in wide, and weighs 100 lb. Plan on two people or a lift for mounting, and check your wall space and working clearance before ordering.
8) Is this a fusible switch or a breaker-type main disconnect?
The 3MFS400RT is a fusible switch: overcurrent protection comes from the fuses you install in the clips, not from a circuit breaker. Choose fusible when you want the high interrupting rating and current limitation of Class T or Class R fuses (this unit ships with Class T clips at 100 kAIC); choose a main breaker unit instead if you want resettable protection without stocking spare fuses.
9) Will the 3MFS400RT serve a 120/208V four-wire panel with a neutral?
Yes, it is built as a three-phase, four-wire device at 120/208V, so it accommodates the neutral needed for 120V line-to-neutral loads downstream.
How fast can I get the B-LINE 3MFS400RT delivered?
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Can I return it if it doesn’t work for me?
Yes—ZenSupply offers a hassle-free return policy. If the product isn’t the right fit,
reach out to our support team for a return authorization or setup a return by following our return instructions.
Does the B-LINE 3MFS400RT come with a warranty?
Absolutely. The B-LINE 3MFS400RT is backed by a manufacturer’s warranty.
For full warranty terms, check the product documentation or Contact Us.
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