You're right, that's a frustrating situation! I can definitely help you think through this. Your question is a common one, and the answer requires careful consideration of several factors

The Short Answer:
Yes, you can install IS barriers and circuits in the same XP (Explosion-Proof) control box as 460 VAC wiring, but it requires strict adherence to regulations and best practices to maintain both the explosion-proof and intrinsically safe integrity of the system. There isn't a single, universal "maximum voltage permitted" number. The key is maintaining separation and preventing fault conditions from energizing the IS circuits.

The Detailed Explanation

Here's a breakdown of the key considerations and why the answer is nuanced:1.

Explosion-Proof Enclosure (XP)

Your control box is designed to contain an explosion within the enclosure and prevent it from propagating to the surrounding hazardous atmosphere. The design and certification (by a recognized testing laboratory like UL, FM, CSA, etc.) are critical for maintaining this protection.2.

Intrinsically Safe (IS) Circuits

IS circuits are designed to be incapable of releasing enough electrical or thermal energy to cause ignition of a hazardous atmosphere, even under fault conditions. This is achieved by limiting voltage and current. IS barriers are key to this protection, limiting voltage and current from non-IS circuits into the hazardous area.3.

Segregation and Separation



2-Inch Rule/Grounded Barrier

You correctly mentioned the 2-inch rule. This is a critical aspect of combining XP and IS. Either maintain a physical separation of at least 2 inches between IS wiring/components and non-IS wiring/components or install a grounded metal barrier. The barrier must be effectively grounded to provide a low-impedance path for fault currents.

Wiring Practices

IS wiring must be clearly identified (typically light blue) and physically separated from non-IS wiring. Use separate raceways, conduits, or cable trays where possible.

Terminations

Use separate terminal blocks for IS and non-IS circuits. Clearly label terminals.4.

Voltage Considerations



The 460 VAC is NOT the limiting factor, as long as it is completely isolated from the IS circuitry. The primary concern is a fault condition within the 460 VAC circuit energizing the IS circuit. Proper insulation, wiring practices, and grounding are key to preventing this. IS Barrier Voltage

The output voltage of your IS barriers is a limiting factor for the field devices connected to the barrier. The barrier's datasheet will specify the maximum allowed voltage (Voc) and current (Isc) that it can deliver to the hazardous area. This needs to be compatible with the intrinsically safe field devices you are using.

Transformer Voltage

Your 115 VAC transformer could pose a risk if it's not properly isolated from the IS circuits. However, running relays from a 115 VAC transformer is a very common and perfectly acceptable practice if that relay is what actuates the IS barrier.

Creepage and Clearance

Creepage (distance along a surface) and clearance (distance through air) are critical for preventing arcing or voltage breakdown between conductors. Ensure that the XP enclosure's design provides adequate creepage and clearance distances between the high-voltage components (460 VAC, 115 VAC) and the IS circuits.5.

Grounding

Proper grounding is absolutely essential. The XP enclosure must be effectively grounded to provide a safe path for fault currents. The IS barrier's ground connection is also critical.6.

Documentation and Certification



Documentation

Keep thorough documentation of the installation, including wiring diagrams, component specifications (especially for IS barriers), and grounding details.

Certification

The modified control box might require re-certification or field labeling by a qualified testing laboratory. This ensures that the modifications have not compromised the explosion-proof or intrinsically safe ratings. This is a very important point.
Key Considerations & Best Practices



Consult with an expert

This type of installation requires expertise in both explosion-proof and intrinsically safe systems. Consult with a qualified electrical engineer experienced in hazardous area installations.

Use certified components

Only use IS barriers and components that are certified for use in the specific hazardous area classification.

Follow manufacturer's instructions

Carefully follow the manufacturer's instructions for installation, wiring, and grounding of all components.

Inspect and maintain

Regularly inspect the control box, wiring, and components to ensure that they are in good condition and that the separation and grounding are maintained.

Consider separate enclosures

If space allows, consider using separate enclosures for the XP and IS systems. This simplifies the installation and reduces the risk of interference.*

Arc Suppression

Consider adding arc suppression to relay coils to minimize electrical noise and potential interference with the IS circuits.

In summary, you can combine XP and IS in a single enclosure, but it's a complex undertaking that requires careful planning, adherence to regulations and best practices, and potentially re-certification. The key is to maintain complete isolation between the high-voltage circuits and the IS circuits and to ensure that a fault condition in the high-voltage circuits cannot energize the IS circuits. Consulting with a qualified expert is strongly recommended.

Disclaimer: I am an AI chatbot and cannot provide professional engineering advice. This information is for general guidance only and should not be substituted for the advice of a qualified expert. Always consult with qualified professionals for specific hazardous area installations. You are responsible for ensuring the safety of your installation. Flag for review