Product Overview
Federal Pacific F3.55 Heater Element for Motor Starter Overload Relays
Condition
Unused, new old stock, clean and in excellent condition. The photographs show one piece from seven angles: five hairpin loops of resistance wire, bright and undistorted, carried between two metal end brackets against a mica insulating plate. Mica is a natural mineral that splits into thin, heat-proof sheets, and its cloudy, mottled grey and amber figure is simply what the mineral looks like - that is the insulator doing its job, not tarnish and not wear. The brown woven-laminate base is intact, the white F 3.55 marking is fully legible, and both brass eyelet terminals are bright, with no fastener bite or arc pitting around either hole. The light yellowish residue at the joints is consistent with the manufacturing techniques employed on this vintage part. Against the ruler the base measures approximately 1-1/2 inches wide.
Same or next business day shipping from our Idaho warehouse. Honest pricing, no nonsense.
Online since 1999. We are here for our customers, with a no-hassle satisfaction guarantee.
Product Overview
The F3.55 is a Federal Pacific thermal overload heater element, the small calibrated piece that sits in a motor starter's overload relay and decides when a motor has been pulling too much current for too long. Motor current passes through the low-resistance element, here five hairpin loops of wire carried between two metal end brackets on a brown woven-laminate card about 1-1/2 inches wide, and the heat that element produces mirrors the heating happening inside the motor windings. When that heat crosses the relay's trip threshold, the relay opens and drops the starter out. Unlike a fuse the heater does not burn open, and unlike a circuit breaker it is protecting the motor rather than the conductor, which is why heaters are selected by motor full load amps instead of wire size. The mottled grey and amber plate standing behind the loops is mica, the natural mineral sheet the industry used for this duty because it insulates without charring at the temperatures a heater element runs at. The base carries the F 3.55 marking in white, and the two brass eyelets serve as both the mounting points and the current path into the relay block. Federal Pacific motor control gear has been out of production for decades, so a correct rebuild usually comes down to finding the matching original heater.
Key Features
- Manufacturer marking: F 3.55, printed in white on the base and clearly legible
- Brand: Federal Pacific (FPE)
- Type: thermal overload heater element for motor starter overload relays
- Element: five hairpin loops of low-resistance wire carried between two metal end brackets
- Insulator: natural mica plate behind the element - the mottled grey and amber figure is the mineral's own appearance, not tarnish
- Base: brown woven-laminate card with two brass eyelet terminals
- Size: base measures approximately 1-1/2 inches wide against the ruler in the photos
- Condition: unused new old stock, clean and excellent, no installation marks on the eyelets or element
- Trip current: not confirmed - match the F 3.55 number to the Federal Pacific heater table for your starter size and motor nameplate amps before use
Applications
- Plant electrician rebuilding a Federal Pacific across-the-line starter and matching heaters to the motor nameplate
- Maintenance tech keeping an obsolete FPE motor control center in service when the OEM parts channel is long gone
- Panel shop restoring vintage industrial control gear that has to go back exactly as built
- Machine restorer returning a mid-century production machine to running order with period-correct protection
Frequently Asked Questions
What does this heater element actually do inside the starter?
It converts motor current into heat that stands in for the heat building inside the motor windings. When the element runs hot enough for long enough, the overload relay it sits in trips and drops the starter out. The heater itself does not open the circuit and does not sacrifice itself the way a fuse does.
What current does an F3.55 trip at?
Not confirmed here. Federal Pacific heaters are selected from a published table that pairs the heater number with a specific starter size and a motor full load amp range, so the same F number can be right in one starter and wrong in another. Check the F 3.55 designation against the heater chart for your starter and your motor nameplate amps before installing.
The plate behind the element looks mottled. Is that tarnish?
No. That plate is mica, and mottled is simply what mica looks like. It is a natural mineral that splits into thin translucent sheets with cloudy grey, amber and pink figure, and it is here because it insulates the element from the base without charring at the temperatures a heater runs at. The faint yellowish residue at the joints is consistent with the manufacturing techniques employed on this vintage part rather than anything picked up in service.
Do the photos show any sign this one was ever installed?
No. This piece is unused new old stock. The brass eyelets are bright and unmarked with no screw bite or arc pitting, the wire loops are straight and evenly spaced, and the marking is crisp. Nothing on it reads as time in a starter. The photographs are the spec here, so look them over and judge for yourself.
I need heaters for one starter. Do I have to buy a full box?
No. A three-pole starter takes one heater per phase, and you can order exactly that many here, plus a spare for the drawer if you want one, instead of chasing a factory carton of ten you will never finish. Our records show six pieces on the shelf; the photographs are of one of them. Shipping is $8 flat rate and free once your order passes $28, and orders leave our Idaho warehouse the same or next business day.
Five hairpin loops of wire on a brown laminate card, built so a motor's own appetite for current is the thing that tells the starter when to let go. Match the F number to your nameplate and this small piece goes back to standing watch over a machine that still has work left in it.
