46 CFR 143.250: System isolation devices and markings

Last reviewed: October 14, 2026

This section requires isolation devices and markings on electrical equipment and on certain piping systems. It also requires an accessible valve on piping that penetrates the hull below the waterline. Color coding may follow ISO 14726:2008(E) or the TSMS applicable to the vessel.

Applies toElectrical equipment and piping for flammable or combustible liquid, seawater cooling, or fire-fighting systems, plus any piping system that penetrates the hull below the waterline.

What it says

  1. Electrical equipment must have circuit isolation and must be marked as described in § 143.400.

    46 CFR 143.250(a)“Electrical equipment must be provided with circuit isolation and must be marked as described in § 143.400.”

  2. Electrical panels or other enclosures containing more than one source of power must have a sign warning of this condition and identifying where to secure all sources.

    46 CFR 143.250(b)“must be fitted with a sign warning persons of this condition and identifying where to secure all sources.”

  3. Piping for flammable or combustible liquid, seawater cooling, or firefighting systems must have isolation valves clearly marked by labeling or color coding that lets the crew identify the function.

    46 CFR 143.250(c)“must be fitted with isolation valves that are clearly marked by labeling or color coding that enables the crew to identify its function.”

  4. Any piping system that penetrates the hull below the waterline must have an accessible valve, located as close to the hull penetration as is practicable, to prevent accidental admission of water into the vessel through the pipe or if the pipe fractures.

    46 CFR 143.250(d)“must be fitted with an accessible valve, located as close to the hull penetration as is practicable”

  5. The valve on hull-penetrating piping must be clearly marked by labeling or color coding that lets the crew identify its function.

    46 CFR 143.250(d)“The valve must be clearly marked by labeling or color coding that enables the crew to identify its function.”

  6. Color coding required by this section may follow ISO 14726:2008(E), or be done in accordance with the TSMS applicable to the vessel.

    46 CFR 143.250(e)“may be met by complying with coding standards contained in the ISO 14726:2008(E)”

Common questions

Do panels with more than one power source need a warning sign?

Yes. Electrical panels or other enclosures containing more than one source of power must have a sign warning of this condition and identifying where to secure all sources.

“Electrical panels or other enclosures containing more than one source of power must be fitted with a sign warning persons of this condition”

Where must the valve on a pipe through the hull below the waterline be placed?

It must be accessible and located as close to the hull penetration as is practicable. It prevents accidental admission of water into the vessel.

“must be fitted with an accessible valve, located as close to the hull penetration as is practicable”

What color coding standard can be used for valve markings?

Color coding may follow the coding standards in ISO 14726:2008(E), or be done in accordance with the TSMS applicable to the vessel.

“or in accordance with the TSMS applicable to the vessel.”

The text of 46 CFR 143.250

Electronic Code of Federal Regulations (eCFR), current as of April 16, 2026 · Read it on eCFR

System isolation and markings

Electrical equipment, piping for flammable or combustible liquid, seawater cooling, or fire-fighting systems must be provided with isolation devices and markings as follows:

(a) Electrical equipment must be provided with circuit isolation and must be marked as described in § 143.400.

(b) Electrical panels or other enclosures containing more than one source of power must be fitted with a sign warning persons of this condition and identifying where to secure all sources.

(c) Piping for flammable or combustible liquid, seawater cooling, or firefighting systems must be fitted with isolation valves that are clearly marked by labeling or color coding that enables the crew to identify its function.

(d) Any piping system that penetrates the hull below the waterline must be fitted with an accessible valve, located as close to the hull penetration as is practicable, for preventing the accidental admission of water into the vessel either through such pipes or in the event of a fracture of such pipe. The valve must be clearly marked by labeling or color coding that enables the crew to identify its function.

(e) Color coding required by this section may be met by complying with coding standards contained in the ISO 14726:2008(E) (incorporated by reference, see § 136.112 of this subchapter), or in accordance with the TSMS applicable to the vessel.

Sections it refers to

The plain-English explanation on this page was written with AI from the regulation text above and checked automatically before publishing: every quote appears in the text, every number comes from it, and a second model confirmed each statement adds nothing the text doesn't say. Regulation text current as of April 16, 2026. The regulation text governs. RegKnot is not affiliated with the U.S. Coast Guard.