PJM reduced voltage 5 percent Monday night as the weather system rolled across its area, which includes 13 states between Illinois and New Jersey, along with the District of Columbia.
Utilities asked large interruptible natural gas customers to switch to alternative fuels, such as diesel or fuel oil, to conserve supplies for "firm" residential and commercial gas customers.
PJM said the system's load reached 138,600 megawatts Tuesday morning around 8 a.m., breaking the 2007 winter peak of 136,675 megawatts.
Natural gas pipelines into New York and New England were running at capacity. Large customers without long-term energy supplies paid steep rates for electricity and gas on the spot markets.
The U.S. Energy Information Agency said that spot-market natural gas prices in New England and New York reached $40 per thousand cubic feet, about 10 times the long-term rate.
The constraints on natural gas supplies spilled over to electricity markets because some power plants that use gas had to curtail generation or had trouble switching to backup fuels. PJM called on power producers to generate "maximum emergency output."
Despite the calls for conservation, PJM and electric utilities said curtailment measures were working as planned. Utilities did not need to resort to rolling blackouts or controlled outages to prevent the system from collapse.
"Our system is performing extremely well with no interruptions due to the extreme weather," said Cathy Engel Menendez, Peco spokeswoman.
Public Service Electric and Gas Co. in New Jersey, which said it did not expect to set a record Tuesday, echoed PJM's call to conserve.
Customers were asked to set thermostats lower than usual, if health permits; postpone using major electric appliances such as stoves, dishwashers, and clothes dryers until after 9 p.m.; and turn off unneeded electric lights and appliances.
UGI Utilities reported that a few hundred customers in Millersville, Camp Hill, Enola, and Mechanicsburg were cut off from gas service after its system lost pressure because of an equipment failure.
The outages included Millersville University, though a spokeswoman said the winter break is scheduled to end on Jan. 21, so no classes were affected.
Unlike electrical outages, where customers can be restored en masse, outages for natural gas customers are more labor-intensive because the utility must reconnect each customer individually to verify service is restored and that equipment is functioning properly.