Mark,You're right to be suspicious of a tap ahead of the main for emergency lighting and control circuits. Here's a breakdown of why this setup likely was common practice, may have been grandfathered, and why it's almost certainly not allowed under current codes

Historical Context (Why it was likely installed):
Reliability

The primary reason for tapping ahead of the main was to ensure that emergency circuits would remain energized even if the main breaker tripped due to an overload in the main load panel. This was seen as a way to ensure the emergency lighting and critical controls would function during power failures in the main distribution system.

Simplicity

It was often simpler (and potentially cheaper at the time) to tap the service conductors directly rather than installing a separate emergency power system.

Code Interpretation

Early electrical codes were less stringent and more ambiguous about separating emergency and normal power systems. Local interpretations varied considerably.

Why it might be "Grandfathered"



Code Compliance at Time of Installation

If the installation met the electrical code requirements in effect at the time it was installed, it might be considered legally non-conforming. This means it wouldn't have to be brought up to current code unless there were substantial renovations or changes to the electrical system that affected the emergency lighting and hood control circuits.

"Grandfathering" Exceptions

Often, local jurisdictions will allow existing installations to remain as long as they are deemed safe and functional. However, this is at the discretion of the AHJ (Authority Having Jurisdiction), typically a local electrical inspector.

Why it is (almost certainly) Not Allowed Now (NEC and Modern Practices)



Separation of Emergency Systems

The NEC (National Electrical Code) strongly emphasizes the separation of emergency and normal power systems. Emergency systems (required by local/state/fed codes) must operate independently of the normal power system.

Dedicated Emergency Power Source

Modern emergency systems typically require a dedicated, reliable power source such as:

Emergency generator

Automatically starts upon loss of normal power.

Battery backup system (UPS)

Provides power for a limited duration.

Separate service (less common)

A completely independent electrical service.

Transfer Switch Requirement

If a generator or battery system is used, an automatic transfer switch (ATS) is required to seamlessly switch the emergency load to the backup power source upon failure of the normal power source.

Overcurrent Protection

Current NEC regulations require emergency circuits to have proper overcurrent protection and be clearly identified and segregated from the normal power distribution system. Tapping ahead of the main violates this principle.

Article 700/701/702 (NEC)

The NEC specifically addresses emergency systems (Art. 700), legally required standby systems (Art. 701), and optional standby systems (Art. 702). These articles mandate the requirements for independent power sources, wiring methods, and control circuits for these systems.

Potential for Failure

A failure in the main switchgear could also affect the emergency system. The emergency system needs to be separate from issues in the main.

Potential Issues with the Existing Setup



Lack of Overcurrent Protection

The 20A fused disconnect is likely the only overcurrent protection for those emergency circuits. A fault on those circuits could potentially damage the service conductors themselves.

Code Violation

As discussed above, it almost certainly violates current NEC requirements.

Reliability Concerns

While the intent was to improve reliability, the lack of redundancy and proper separation makes the system vulnerable to failures in the main switchgear.

Safety Hazard

Improperly installed and maintained taps can be fire hazards.

Recommendations


Consult a Licensed Electrical Contractor

The first and most important step is to have a qualified and licensed electrical contractor evaluate the existing installation. They can perform a thorough inspection, determine if it meets any grandfathering criteria, and provide recommendations for bringing the system up to code.2.

Contact Your Local AHJ (Electrical Inspector)

The local electrical inspector has the final say on whether the installation is acceptable. They may require specific modifications to comply with current codes.3.

Consider a Proper Emergency Power System

The best long-term solution is to install a dedicated emergency power system with a generator or battery backup and automatic transfer switch. This will ensure a reliable and code-compliant emergency power source.4.

Document Everything

Keep detailed records of all inspections, repairs, and modifications to the electrical system. This documentation will be helpful for future inspections and maintenance.

Photos

Yes, photos would absolutely help. Please include clear pictures of: The entire electrical service entrance (where the 600A main is located). The fused disconnect (the 20A Edison type). How the wires are tapped from the service conductors. (Close-ups are critical here). The panel or equipment that the fused disconnect feeds.* Any labeling or markings on the disconnect or related equipment.

In summary, while the setup might have been common practice in the past, it's highly unlikely to be compliant with current codes and should be thoroughly evaluated and upgraded by a qualified professional. Prioritizing safety and compliance is essential, and this means separating the emergency system from the normal power system. Flag for review