What to Do When Siemens 3TF48 Replacement Parts Are Unavailable

When a Siemens 3TF48 part can no longer be bought from the OEM, find out which component has failed and replace that component with an aftermarket equivalent. The 3TF48 is a discontinued 3-pole World Series contactor, and BRAH Electric lists a replacement for the complete contactor and, separately, for its coil, main contact kit, arc chute, auxiliary contact block and 3UA58 overload relay. A retrofit to a different contactor family is seldom the first step.

The sections below help you decide which part has failed, give the BRAH part number for each one in a single table, and list what to confirm before you order.

3TF48 parts at a glance

• Copy the full number from the nameplate of the contactor and from the label of the part that failed. The BRAH number is the Siemens number with a B in front.
• Diagnose before you buy. A 3TF48 that will not close may need only a coil, and one that runs hot may need only contacts.
• Replace the complete contactor when more than one of its parts is damaged, or when the frame itself is cracked, burnt or binding.
• The overload relay is a separate device mounted with the contactor. Its part number starts with 3UA, and it is ordered by current range.
• For anything not in the table, call (855) 355-2724 with the part number.

Find the 3TF48 component that failed

Start with what the starter does, then confirm by inspection with the power locked out. Each heading below is one row of the parts table that follows.

Coil

The contactor does not pull in although the correct control voltage is present at coil terminals A1 and A2, or it pulls in and drops out. A burnt coil is often discoloured, smells of overheated insulation, or measures open circuit with the control wiring disconnected. If the voltage at A1 and A2 is missing or low, the fault is in the control circuit and a new coil will not cure it. Choosing the coil is covered in the guide to coil voltage for a 3TF48 replacement.

Main contacts

The contactor closes but the motor runs on unequal phase currents, a pole runs hot, or the contacts stay closed after the coil is released. Look for heavy pitting, contact material worn thin, or contacts welded together. Light discolouration and a slightly roughened surface are normal on contacts that have switched load. A contact kit replaces the contacts of all three poles together.

Arc chute

The arc chute sits over the main contacts and cools and splits the arc each time they open. Replace it if it is cracked, if its plates are burnt away or loose, or if it shows tracking marks across the insulation. Never run the contactor with the arc chute removed. For background, see what an arc chute does.

Auxiliary contact block

The main contacts work but the control circuit misbehaves: the starter will not seal in when the start button is released, an interlock does not release, or a run signal to a PLC or pilot light is missing. Check continuity through each auxiliary contact with the contactor open and then held closed by hand, power off.

Overload relay

The relay trips with the measured current in all three phases below its setting, will not reset after it has cooled, or shows heat damage at its terminals. A relay that trips on a real overload is not faulty. The checks to run first are in the overload relay troubleshooting guide.

Complete contactor

The moving parts stick or bind when operated by hand with the power off, the housing is cracked or heat-damaged, a terminal is burnt, or several of the parts above have failed together. In those cases a complete replacement contactor is usually the sounder repair.

BRAH replacement for each 3TF48 component

One row for each component. The linked part numbers open the product pages.

Notes on the table:

• Contactor. The seven listings differ in the coil voltage they are supplied with: 24VAC, 110/120VAC, 208VAC, 240VAC or 480VAC. Order by the full Siemens number including its suffix. The 75A and 60HP figures are catalogue ratings. Match the replacement to the contactor nameplate and the motor nameplate, and do not read them as a motor rating for your application.
• Coil. Choose the row whose voltage matches the control circuit, not the motor supply.
• Contact kit. The kit is listed for the 3TF48 at the same 75A catalogue rating as the contactor. Confirm the number on your contactor before ordering.
• Auxiliary contact. The two listings carry the same catalogue description. Order the one whose number matches the block you are removing.

The other 3TF sizes, with their coils and arc chutes, are in the guide to Siemens 3TF contactor replacement options.

3UA58 overload relays listed for the 3TF48

The catalogue names the 3TF46, 3TF47, 3TF48 and 3TF49 in the description of each 3UA58 relay. Pick the row whose range includes the full-load current on the motor nameplate, or order the same number as the relay you are removing. After fitting, set the dial to the motor nameplate current.

Other relay series are under overload relays.

Repair the 3TF48 or replace it complete

Replacing one component is quicker to fit and leaves the power wiring undisturbed in most cases. It suits a contactor that is otherwise clean and moves freely. A complete contactor makes more sense when the contacts and the arc chute are both damaged, when a fault has overheated the housing, or when the contactor has reached the point where one part after another is wearing out.

Either way, a like-for-like part keeps the starter as it was designed: the same mounting, the same terminals and the same overload relay. Changing to a different contactor family means new mounting holes, different terminal positions, a different overload relay and revised drawings. Keep that for a panel where several devices are obsolete or damaged, not for one failed part.

While the starter is open, look at what surrounds the failed part. Check the tightness of the power terminals, the condition of the control wiring insulation, and the overload relay terminals. A loose connection that overheated one part will overheat its replacement.

Before you order 3TF48 parts

• The full contactor number from the nameplate, including the suffix after the dash.
• The number printed on the failed part: 3TY7 for a coil, contact kit, arc chute or auxiliary contact, 3UA for an overload relay.
• The control voltage at the coil, and whether it is AC.
• The motor nameplate full-load current and horsepower.
• How many auxiliary contacts the control circuit uses, normally open and normally closed.
• The mounting and terminal layout of the installed part, compared with the product page.

BRAH Electric is an aftermarket manufacturer and is not an authorized Siemens distributor. It designs its parts in-house and tests them at its Carlsbad, California facility. Parts carry a 2-year warranty from the date of invoice, except contact kits, which carry 6 months. Returns are accepted within 30 days of shipment with an RMA and are subject to a restocking charge of 25 to 50 percent, so confirm the part number before ordering. In-stock orders placed before 3:00 PM Pacific ship the same business day. Phone support is available Monday to Friday, 6AM to 5PM Pacific.

Planning spares for a 3TF48 starter

A failed part is the moment to record what the starter needs. Write down the contactor number, the coil number and voltage, and the overload relay number and setting, and keep the list with the panel drawings. For a starter that production depends on, a spare coil and a contact kit on the shelf cost little next to an unplanned stop. Inspect contactors that switch often on a regular schedule so that worn contacts are found before they weld.

Safety when working on a 3TF48 starter

Opening a contactor exposes line terminals that stay live until the supply is isolated upstream. Before any inspection or part change, de-energize the starter, apply lockout/tagout, and verify the absence of voltage on the power terminals and on the control circuit, which can be fed from a separate source. The work is for qualified personnel. After reassembly, check that the arc chute is seated and the contactor moves freely by hand before restoring power, then watch the first few starts.

Siemens 3TF48 parts FAQs

Is the Siemens 3TF48 still made?

No. Siemens has discontinued the 3TF series and the BRAH catalogue marks the 3TF48 as obsolete. Aftermarket replacements for the contactor and its parts are available.

Do I have to replace the whole contactor if one part fails?

No. The coil, the contact kit, the arc chute and the auxiliary contact block are each listed as separate parts for the 3TF48. Replace the complete contactor when several parts or the frame are damaged.

Can I fit a contactor from a different manufacturer?

It can be done, but it is a redesign and not a repair. The mounting, terminals, coil, auxiliary contacts and overload relay all have to be matched again and the drawings updated. A direct replacement for the 3TF48 avoids that work.

What can go wrong with a substitute that is not an exact match?

A coil of the wrong voltage burns out or fails to close the contactor. A contactor with a lower rating overheats. A different frame may not accept the existing overload relay, which leaves the motor without the protection it was set up with.

Which overload relay goes with a 3TF48?

The catalogue lists the 3UA58 series for the 3TF48, in twelve current ranges from 4 to 6.3 A up to 70 to 88 A. Choose the range that includes the motor full-load current.

How long is the warranty on replacement 3TF48 parts?

BRAH parts carry a 2-year warranty from the date of invoice. Contact kits carry a 6-month warranty.

References

• IEC 60947-4-1, Low-voltage switchgear and controlgear: contactors and motor-starters. The product standard for electromechanical contactors and the overload relays used with them.
• OSHA 29 CFR 1910.147, The control of hazardous energy (lockout/tagout). The US rule for isolating equipment before servicing.
• NFPA 70B, Standard for Electrical Equipment Maintenance. Covers the inspection and maintenance of electrical equipment.