## Facts

- Southwire Company used industrial equipment that had been manufactured and/or supplied by Beloit Eastern Corporation.
- An accident occurred during operation that damaged equipment and resulted in claimed losses.
- Southwire alleged the equipment (or a component part) was defective when it left Beloit’s control and sought recovery on product-defect and negligence theories under Pennsylvania law.
- Beloit disputed that any actionable defect existed at the time of sale and contended that changes made after sale and the way the equipment was used or maintained were responsible for the accident.
- A central dispute in the case was how to treat the purchaser’s post-sale alteration of the equipment: whether it automatically relieved the manufacturer/supplier of responsibility, or whether liability turned on whether the alteration was a foreseeable intervening act (as opposed to an unforeseeable “supervening” cause).

## Issues

1. Under Pennsylvania products-liability and negligence principles, does a purchaser’s post-sale alteration of equipment automatically relieve the manufacturer/supplier of liability for an ensuing accident?
2. If not automatic, when does a post-sale alteration constitute a supervening (superseding) cause that breaks the chain of proximate causation?

## Decision

- The court analyzed the post-sale alteration question using intervening/supervening cause concepts rather than treating alteration as an automatic defense.
- The court held that a post-sale alteration cuts off liability only if it is sufficiently unforeseeable and causally responsible for the loss so as to constitute a supervening cause.
- Applying that framework to the record before it, the court resolved the liability dispute in favor of Beloit.

## Legal Principles

- Post-sale alteration of a product is not, by itself, a complete defense; the effect of the alteration is evaluated through proximate-cause analysis.
- An intervening act (including a purchaser’s modification) becomes a supervening/superseding cause only when it is not reasonably foreseeable and is of a character that makes it unfair to attribute the resulting harm to the manufacturer/supplier.
- In product-defect and negligence claims, the plaintiff must still connect the claimed defect to the loss; when the evidence supports alternative causal explanations tied to later modification or use, the plaintiff’s proof of causation may fail.

## Conclusion

*Southwire Co. v. Beloit Eastern Corp.* treats a purchaser’s post-sale modification as a causation problem, not a per se bar: the manufacturer/supplier is relieved of liability only when the modification is an unforeseeable supervening cause of the accident, and the court ultimately ruled for Beloit under that approach.


Southwire Co. v. Beloit Eastern Corp., 370 F.Supp. 842 (1974)