McGraw-Edison 550-BLS Insulating Collar Kit

Overview

Insulating standoff collar kit for the McGraw-Edison 550-BLS load tap changer, also cataloged 550B and BHS. The kit carries the switch’s insulating standoff collars, insulating tubes, and locking pins for one complete unit.

Machined from G10, not wood

The original McGraw-Edison collars were a wood-based laminate. In hot transformer oil that material takes on moisture, swells, and loses dimensional stability over time, which lets the contact stack drift out of alignment. Southern Switch machines the collars from G10, a glass-cloth epoxy laminate that holds its dimensions and dielectric strength in oil and does not swell or delaminate, so the insulating stack stays true for the life of the switch.

Standoff collars, insulating tubes, and locking pins for one complete 550-BLS switch, with the McGraw-Edison OEM reference for each. Quantities are per complete kit.

About the McGraw-Edison 550

The McGraw-Edison 550 is a reactance-type arcing tap switch and one of the most widely deployed LTCs in utility power transformers across North America. During a tap change the contacts bridge two taps briefly through a preventive autotransformer that limits the circulating current, and the arcing contacts open and close under load current on every operation. The main moving contact, stationary contact, and reversing switch contacts bear that duty on every tap change. At 50,000 operations or the manufacturer's recommended inspection interval, contact condition directly determines whether the tap changer will perform reliably between outages.

Why replace worn LTC contacts

Worn or burned tap-changer contacts raise resistance, run hot, and can lead to tap-changer failure. Precision replacements restore reliable switching and extend the service life of the LTC.

Stock, lead time & reverse engineering

Lead time is confirmed at quote; discontinued or hard-to-find parts are reverse-engineered from a sample, a drawing, or a model number. Based in Palm Harbor, FL, Southern Switch & Contacts manufactures and ships replacement parts to utilities nationwide, and has served the industry since 1982.