Okay, this is a common situation in electrical work, and understanding the reasoning behind it is crucial. Here's a breakdown of why the engineer might have oversized the service and what you should do

Possible Reasons for Oversizing the Service:
Future Expansion

This is the most likely reason. Medical facilities often expand or upgrade equipment. The engineer may have anticipated that the CAT scan machine might be upgraded to a more powerful model in the future, or that other equipment may be added to the same electrical panel. Oversizing the service now saves a lot of money and disruption later when upgrades are required.

Demand Factor

CAT scan machines don't run at their full rated load continuously. Demand factors allow for a calculated reduction in the overall load based on how often equipment is actually used at its maximum rating. However, engineers often err on the side of caution, especially in critical applications like medical imaging. They may have used a more conservative demand factor than strictly necessary.

Motor Starting

CAT scan machines contain motors (for the gantry rotation, table movement, cooling systems, etc.). Motors draw significantly higher current during startup (inrush current) than their normal running current. The engineer may have oversized the service to accommodate these high inrush currents without causing voltage dips or other problems.

Specific Code Requirements or Hospital Standards

Some jurisdictions or hospital systems have more stringent electrical design requirements than the minimum code. They may mandate a certain level of redundancy or capacity beyond the calculated load.

Harmonic Distortion

Modern electronic equipment (like CAT scans) can generate harmonic currents, which can put additional stress on the electrical system. An oversized service can help mitigate the effects of harmonics.

Voltage Drop

A larger conductor size (associated with the 225A service) will reduce voltage drop, which is particularly important in a high-current, sensitive environment like a medical facility.

Load Diversity

The facility may have other loads connected to the same main electrical panel that the CAT scan is connected to. The engineer may have sized the main to account for the total load of the entire panel.

Will Following the Drawings Be a Problem? No, it will not be a problem to install the 225 amp service as specified in the drawings, as long as the disconnect at the CAT scan itself is appropriately sized for 125 amps. In fact, it will provide a more robust and reliable system. It's generally better to err on the side of oversizing for electrical infrastructure, especially in critical applications. An undersized system can lead to nuisance tripping, equipment failure, and safety hazards. An oversized system is generally just a cost issue (slightly more expensive materials).

What You Should Do


Verify Disconnect Size

Double-check the CAT scan disconnect rating again to ensure it is indeed 125 amps. Verify this information from multiple sources (the equipment nameplate, the manufacturer's documentation).2.

Follow the Drawings

Install the 225 amp service, feeders, and overcurrent protection as specified in the engineer's drawings. This is the most important thing.3.

Consult the Engineer (Ideal)

If possible, contact the project engineer and ask about the reason for the oversized service. Understanding their reasoning will give you more confidence in the design. They can clarify their assumptions and calculations.4.

Ensure Proper Overcurrent Protection

Make sure the overcurrent protection devices (circuit breakers or fuses) are correctly sized for the conductor ampacity and the equipment they protect. The 225 amp service will have a 225 amp breaker at the meter main. The feeders going to the CAT scan will have appropriate overcurrent protection at their origin, even though the main disconnect is rated for 125A.5.

Proper Termination

Ensure all conductors are properly terminated with appropriately sized lugs and connectors.6.

Document Everything

Keep detailed records of all your work, including conductor sizes, overcurrent protection ratings, and any deviations from the original drawings (if any are made with approval).

Key Considerations



Coordination

Ensure proper coordination of the overcurrent protection devices (main breaker, feeder breakers, disconnect fuse/breaker). This means the devices are selected so that a fault closer to the load will trip the local breaker first, minimizing disruption to the rest of the system.*

Code Compliance

Ensure all work complies with the applicable electrical codes (NEC or local equivalent).

In summary, follow the engineered drawings. The 225 amp service will not harm the CAT scan equipment (as long as the disconnect is rated appropriately and properly protected). It likely provides additional capacity for future expansion or to account for other factors that the engineer considered. Contacting the engineer for clarification is always a good practice if possible. Flag for review