Don’t blow a fuse – Or should you? Wenatchee Home Inspection

Published by Don Hester on January 31, 2021January 31, 2021

When evaluating older homes often you will find remnants of electrical systems past. On this home inspection it was just that case.

Here is an example of a old fused panel with what is referred to as “Edison” style fuses. The issue with “Edison” style fuses is they cannot be on circuit more than 125 v and not rated more than 30 AMP. In addition there are some other restrictions on their use. The big one is they must not be tampered with.

In this case that is not true/ We have 30 AMP fuses on branch circuits where 20 AMP or less is required. We have one conductor showing signs of overheating. This is a very dangerous installation due to the fact that now the wire (conductor) is the weak link in the system. If the circuit is overloaded the wire will start acting like a  resistive heater which can lead to fire. This is why the rules are very specific to the instillation of these type of fuses.

So take a look at the code. 

From the 2020 NEC- 

240.51 Edison-Base Fuses

(A) Classification.
Plug fuses of the Edison-base type shall be classified at not over 125 volts and 30 amperes and below.

(B) Replacement Only.

Plug fuses of the Edison-base type shall be used only for replacements in existing installations where there is no evidence of overfusing or tampering.

240.52 Edison-Base Fuse holders

Fuse holders of the Edison-base type shall be installed only where they are made to accept Type S fuses by the use of adapters.

Edison-base fuses are classified to operate at not more than 125V and have an ampere rating of not more than 30A [240.51(A)]. In addition, the fuses are permitted only for replacement in an existing installation where there’s no evidence of tampering or overfusing [240.51(B)]. Edison-base fuse holders must be used only if they’re made to accept Type S fuses by the use of adapters [240.52].

Type S adapters are designed to fit Edison-base fuse holders [240.54(A)], and must be designed for Type S fuses only [240.54(B)]. Type S adapters are designed so they can’t be removed once installed [240.54(C)]. Type S fuses, fuse holders and adapters must be designed so that tampering or shunting would be difficult [240.54(D)]. Dimensions of Type S fuses, fuse holders, and adapters shall be standardized to permit interchangeability regardless of the manufacturer [240.54(E)].

240.53 Type S Fuses
Type S fuses shall be of the plug type and shall comply with 240.53(A) and (B).

(A) Classification.
Type S fuses shall be classified at not over 125 volts and 0 to 15 amperes, 16 to 20 amperes, and 21 to 30 amperes.

(B) Noninterchangeable.
Type S fuses of an ampere classification as specified in 240.53(A) shall not be interchangeable with a lower ampere classification. They shall be designed so that they cannot be used in any fuseholder other than a Type S fuse holder or a fuse holder with a Type S adapter inserted.

240.54 Type S Fuses, Adapters, and Fuse holders

(A) To Fit Edison-Base Fuse holders.
Type S adapters shall fit Edison-base fuse holders.

(B) To Fit Type S Fuses Only.
Type S fuse holders and adapters shall be designed so that either the fuse holder itself or the fuse holder with a Type S adapter inserted cannot be used for any fuse other than a Type S fuse.

(C) Nonremovable.
Type S adapters shall be designed so that once inserted in a fuse holder, they cannot be removed.

(D) Nontamperable.

Type S fuses, fuse holders, and adapters shall be designed so that tampering or shunting (bridging) would be difficult.

(E) Interchangeability.

Dimensions of Type S fuses, fuse holders, and adapters shall be standardized to permit interchangeability regardless of the manufacturer.

So this situation needs to be corrected and quickly. Ideally replacement with a new panel would be best which will solve several issues going on here. In addition to the over-fusing we have lugs that have been double lugged (double-tapped), which is also not allowed unless the terminal is rated for more than one conductor.

Quote of the Day


“Eye of newt, and toe of frog, Wool of bat, and tongue of dog, Adder’s fork, and blind-worm’s sting, Lizard’s leg, and owlet’s wing, For a charm of powerful trouble, Like a hell-broth boil and bubble. Double, double toil and trouble; Fire burn, and caldron bubble.”

William Shakespeare

If you find any errors or have additional information that would expand on any code, building standards or manufacturer requirements please let me know.

NCW Home Inspections, LLC  is a Licensed Washington State Home Inspection service located in Wenatchee Washington serving Chelan County, Douglas County, Kittitas County, Okanogan County and Grant County Washington and the cities of Wenatchee, Leavenworth, Cashmere, Oroville, Cle Elum, East Wenatchee, Quincy and many more…  

Your Wenatchee and Chelan Professional Real Estate, Home and Structural Pest Inspection Service

Coordinator & Instructor- Fundamentals of Home Inspection-  Bellingham Technical College

Former WA Home Inspector Advisory Licensing Board

www.ncwhomeinspections.com                                                   509-670-9572

 You can follow me on Facebook, Twitter, Google+ and on my website Blog.

If you find any errors or have additional information that would expand on any code, building standards or manufacturer requirements please let me know.

NCW Home Inspections, LLC  is a Licensed Washington State Home Inspection service located in Wenatchee Washington serving Chelan County, Douglas County, Kittitas County, Okanogan County and Grant County Washington and the cities of Wenatchee, Leavenworth, Cashmere, Oroville, Cle Elum, East Wenatchee, Quincy and many more…  

Your Wenatchee and Chelan Professional Real Estate, Home and Structural Pest Inspection Service

Coordinator & Instructor- Fundamentals of Home Inspection-  Bellingham Technical College

Former WA Home Inspector Advisory Licensing Board

www.ncwhomeinspections.com                                                   509-670-9572

 You can follow me on Facebook, Twitter, Google+ and on my website Blog.

(Click on Icons to go to social media pages.)