Ferbose
Headphoneus Supremus
- Joined
- Jun 27, 2004
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When audiophile power cords are being advertised, the term "hospital grade plug" is often mentioned. Hospitals have lots of sensitive and big electronic equipment that can't afford to fail. So it makes sense to use good power cords in hospitals, right? But that got me thinking: what kind of power cords do they actually use in hospitals? After doing a lot of market search, these are facts I have gathered about North American hospital grade replacement power cords.
1. They come with NEMA 5-15P hospital grade plugs and IEC-60320-C13 connectors
2. They use three-conductor cables, mostly 8-12 feet long.
3. Most of them are made of 18 AWG wires, and a few with 16 AWG
4. They must meet UL and CSA approvals to qualify as hospital grade power cords
5. Usually the plug has a green dot on it to show it has been properly tested
6. These power cords have no shielding
7. Sometimes the plugs are transparent so the integrity of the connections inside can be directly examined
8. All the certified cords I found have pre-molded plugs. Big, round plugs from Marinco or Hubbell are generally sold by individually for custom assemblies.
9. Special "low-leakage" cords are available. These use special wires and plugs to ensure that the current leaking to the ground is minimal. These cords are used in certain equipment to reduce the risk of electric shock to the patient.
With these facts in mind, it is interesting to compare them with audiophile grade power cords. Audiophile power cords like to emphasize on thick wires (10-14 AWG), shielding (or twisted pair construction to enhance EMI/RF rejection), hospital grade plugs and pleasant aesthetics. Sometimes, audiophile power cords also emphasize on special materials (especially silver) or construction. Let me examine some of the major differences between hospital grade and audiophile power cords.
1. Wire Gauge.
Audiophile cord vendors like to emphasize that heavy wires lower DC resistance. 10 feet, 16 AWG wire has impedance of 0.040 ohms. Going to 12 AWG reduces impedance to 0.016 ohms. But house AC outlet generally has impedance of 0.2 ohms in the US. Other house appliances drawing currents will cause the AC impedance to go even higher, as well as lower the power factor, making it harder for audio amplifiers to draw large currents during peak demands. Hence, AC line impedance problem need to be addressed with power conditioners. Most hi-end UPS systems have active power factor correction. Some audio power conditioners also have power factor correction, from companies such as Furman or PS Audio.
2. Shielding
I could not find a single hospital grade power cord that has shielding. Many hi-end power cords have shielding. Since power cords carry a lot of power, it is unlikely RF and EMI will really affect the current flow in the power cord. The purpose of shielding is probably to prevent EMI from interfering with small-signal wires in the system. Anyway, I am not sure why hospital grade power cords don't have shielding, but in my experience shielded power cords work better in my current system. You could always add some ferrite clamps to any power cord to facilitate RF rejection though.
3. Certification
I feel that one of the most important things in cables is to have good contacts, both internally and externally. Good contact between the wires and connectors is really crucial and so is the contact between the cord and the equipment and outlet. Hospital grade power cords are actually tested for good connectivity and safety. Most audio power cords do not received any official approval from UL or CSA. It is not economical for power cords made in small quantities to obtain such certifications. In some countries it is illegal to use uncertified power cords. Here in the US there is no law against that, but there may be a problem with the insurance company if it causes a fire.
4. Wire Material
All hospital power cords I find use multi-stranded, standard-quality copper. In contrast, many hi-end power cords use high purity OFC, single crystal copper, silver-plated copper or silver. Audiophile cords may also be constructed with solid-core wire or hollow wire or even ribbon wires.
Lastly, when protection from dirty AC power is required in the hospital, surge protectors and power conditioners are used. Tripp-Lite basically dominates the power-treatment market for hospitals. Lower-end Tripp Lite offers are surge protection power bars. The midrange stuff is based on isolation transformers. The high end stuff is UPS system with AC-DC-AC conversion. For the audiophile market, there are many brands of boutique power conditioners. It is kind of worrying that most of audiophile power conditioners are not UL certified and no one knows if they could be potential fire hazards.
In summary, it is quite educational for me to see how hospitals deal with AC power. In hospitals, sensitive electronic equipment is used in critical situations where human lives are at stake. No voodoo and no snake-oil are allowed in that business for sure! I don't believe that hospital power cords and conditioners are the best solutions for all audio systems. But I think we can all take some lessons from how hospitals actually deal with AC problems, so we won't be swayed so easily by the dubious claims of all-too-many audiophile boutique products.
1. They come with NEMA 5-15P hospital grade plugs and IEC-60320-C13 connectors
2. They use three-conductor cables, mostly 8-12 feet long.
3. Most of them are made of 18 AWG wires, and a few with 16 AWG
4. They must meet UL and CSA approvals to qualify as hospital grade power cords
5. Usually the plug has a green dot on it to show it has been properly tested
6. These power cords have no shielding
7. Sometimes the plugs are transparent so the integrity of the connections inside can be directly examined
8. All the certified cords I found have pre-molded plugs. Big, round plugs from Marinco or Hubbell are generally sold by individually for custom assemblies.
9. Special "low-leakage" cords are available. These use special wires and plugs to ensure that the current leaking to the ground is minimal. These cords are used in certain equipment to reduce the risk of electric shock to the patient.
With these facts in mind, it is interesting to compare them with audiophile grade power cords. Audiophile power cords like to emphasize on thick wires (10-14 AWG), shielding (or twisted pair construction to enhance EMI/RF rejection), hospital grade plugs and pleasant aesthetics. Sometimes, audiophile power cords also emphasize on special materials (especially silver) or construction. Let me examine some of the major differences between hospital grade and audiophile power cords.
1. Wire Gauge.
Audiophile cord vendors like to emphasize that heavy wires lower DC resistance. 10 feet, 16 AWG wire has impedance of 0.040 ohms. Going to 12 AWG reduces impedance to 0.016 ohms. But house AC outlet generally has impedance of 0.2 ohms in the US. Other house appliances drawing currents will cause the AC impedance to go even higher, as well as lower the power factor, making it harder for audio amplifiers to draw large currents during peak demands. Hence, AC line impedance problem need to be addressed with power conditioners. Most hi-end UPS systems have active power factor correction. Some audio power conditioners also have power factor correction, from companies such as Furman or PS Audio.
2. Shielding
I could not find a single hospital grade power cord that has shielding. Many hi-end power cords have shielding. Since power cords carry a lot of power, it is unlikely RF and EMI will really affect the current flow in the power cord. The purpose of shielding is probably to prevent EMI from interfering with small-signal wires in the system. Anyway, I am not sure why hospital grade power cords don't have shielding, but in my experience shielded power cords work better in my current system. You could always add some ferrite clamps to any power cord to facilitate RF rejection though.
3. Certification
I feel that one of the most important things in cables is to have good contacts, both internally and externally. Good contact between the wires and connectors is really crucial and so is the contact between the cord and the equipment and outlet. Hospital grade power cords are actually tested for good connectivity and safety. Most audio power cords do not received any official approval from UL or CSA. It is not economical for power cords made in small quantities to obtain such certifications. In some countries it is illegal to use uncertified power cords. Here in the US there is no law against that, but there may be a problem with the insurance company if it causes a fire.
4. Wire Material
All hospital power cords I find use multi-stranded, standard-quality copper. In contrast, many hi-end power cords use high purity OFC, single crystal copper, silver-plated copper or silver. Audiophile cords may also be constructed with solid-core wire or hollow wire or even ribbon wires.
Lastly, when protection from dirty AC power is required in the hospital, surge protectors and power conditioners are used. Tripp-Lite basically dominates the power-treatment market for hospitals. Lower-end Tripp Lite offers are surge protection power bars. The midrange stuff is based on isolation transformers. The high end stuff is UPS system with AC-DC-AC conversion. For the audiophile market, there are many brands of boutique power conditioners. It is kind of worrying that most of audiophile power conditioners are not UL certified and no one knows if they could be potential fire hazards.
In summary, it is quite educational for me to see how hospitals deal with AC power. In hospitals, sensitive electronic equipment is used in critical situations where human lives are at stake. No voodoo and no snake-oil are allowed in that business for sure! I don't believe that hospital power cords and conditioners are the best solutions for all audio systems. But I think we can all take some lessons from how hospitals actually deal with AC problems, so we won't be swayed so easily by the dubious claims of all-too-many audiophile boutique products.
